U.S. Fossil Fuel Resources:
Terminology, Reporting, and Summary
Gene Whitney
Section Research Manager
Carl E. Behrens
Specialist in Energy Policy
Carol Glover
Information Research Specialist
October 28, 2009
Congressional Research Service
7-5700
www.crs.gov
R40872
CRS Report for Congress
P
repared for Members and Committees of Congress

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U.S. Fossil Fuel Resources: Terminology, Reporting, and Summary

Summary
Discussions of U.S. and global energy supply refer to oil, natural gas, and coal using several
terms that may be unfamiliar to some. The terms used to describe different types of fossil fuels
have technically precise definitions, and misunderstanding or misuse of these terms may lead to
errors and confusion in estimating energy available or making comparisons among fuels, regions,
or nations.
Fossil fuels are categorized, classified, and named using a number of variables. Naturally
occurring deposits of any material, whether it is fossil fuels, gold, or timber, comprise a broad
spectrum of concentration, quality, and accessibility (geologic, technical, and cultural).
Terminology is adopted to reflect those characteristics.
For oil and natural gas, a major distinction in measuring quantities of energy commodities is
made between proved reserves and undiscovered resources. Proved reserves are those amounts of
oil, natural gas, or coal that have been discovered and defined, typically by drilling wells or other
exploratory measures, and which can be economically recovered. In the United States, proved
reserves are typically measured by private companies, who report their findings to the Securities
and Exchange Commission because they are considered capital assets. In addition to the volumes
of proved reserves are deposits of oil and gas that have not yet been discovered, and those are
called undiscovered resources. The term has a specific meaning: undiscovered resources are
amounts of oil and gas estimated to exist in unexplored areas. If they are considered to be
recoverable using existing production technologies, they are referred to as undiscovered
technically recoverable resources (UTRR). In-place resources are intended to represent all of the
oil, natural gas, or coal contained in a formation or basin without regard to technical or economic
recoverability.
In the United States, certain institutions are designated to determine and report quantities of oil,
natural gas, and coal reserves and undiscovered resources. Other institutions also estimate these
values, but differences in estimating methodology can produce significantly different values.
U.S. proved reserves of oil total 21.3 billion barrels and reserves of natural gas are 237.7 trillion
cubic feet. Undiscovered technically recoverable oil in the United States is 145.5 billion barrels,
and undiscovered technically recoverable natural gas is 1,162.7 trillion cubic feet. The
demonstrated reserve base for coal is 489 billion short tons, of which 262 billion short tons are
considered technically recoverable.
Comparisons of different fuel types can be made by converting all of them to a common unit,
such as barrels of oil equivalent, based on their heat content. The amounts of fossil fuels found in
other nations as reserves and undiscovered resources are much more difficult to determine
reliably because data are sometimes lacking or unreliable, but gross comparisons of national
endowments can be made using available data.

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U.S. Fossil Fuel Resources: Terminology, Reporting, and Summary

Contents
Introduction ................................................................................................................................ 1
Characteristics of Fossil Fuels ..................................................................................................... 1
Terminology ............................................................................................................................... 3
Proved Reserves and Undiscovered Resources ...................................................................... 4
The Importance of Terminology: The Example of the Bakken Formation ........................ 5
Conventional Versus Unconventional Oil and Natural Gas Deposits ...................................... 5
Authoritative Data Sources for U.S. Fossil Fuel Reserves and Resources..................................... 6
U.S. Oil and Natural Gas Reserves and Resources ....................................................................... 8
Proved Reserves.............................................................................................................. 8
Undiscovered Oil and Natural Gas Resources.................................................................. 9
Sub-Economic Oil and Natural Gas Resources .................................................................... 10
Shale Oil....................................................................................................................... 10
Shale Gas...................................................................................................................... 11
Methane Hydrates ......................................................................................................... 11
Heavy Oil ..................................................................................................................... 12
U.S. Coal Reserves and Resources ............................................................................................ 13
Expressing Fossil Fuels as Barrels of Oil Equivalent (BOE) ...................................................... 14
A Brief Overview of Global Fossil Fuel Resources.................................................................... 15
U.S. Production and Consumption of Oil, Natural Gas, and Coal............................................... 20
Key Terms Used in Oil Statistics ................................................................................... 22

Figures
Figure 1. The Resource Pyramid Concept .................................................................................... 2
Figure 2. Resource Pyramid for U.S. Oil ..................................................................................... 3

Tables
Table 1.Onshore U.S. Oil, Natural Gas, and Natural Gas Liquids................................................. 9
Table 2.Offshore U.S. Oil and Natural Gas .................................................................................. 9
Table 3.Total U.S. Endowment of Technically Recoverable Oil and Natural Gas ....................... 10
Table 4.U.S. fossil fuel reserves and resources expressed as BOE.............................................. 14
Table 5.Total Fossil Fuel Reserves of Selected Nations.............................................................. 17
Table 6. Reserves of Fossil Fuels Plus Technically Recoverable Undiscovered Oil and
Natural Gas............................................................................................................................ 19
Table 7.United States Annual Consumption of Oil, Natural Gas, and Coal ................................. 20

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U.S. Fossil Fuel Resources: Terminology, Reporting, and Summary

Appendixes
Appendix. Definition of Terms .................................................................................................. 21

Contacts
Author Contact Information ...................................................................................................... 25

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U.S. Fossil Fuel Resources: Terminology, Reporting, and Summary

Introduction
Current discussions of U.S. and global energy supply refer to oil, natural gas, and coal using
several terms that may be unfamiliar to some. The terms used to describe different types of fossil
fuels have technically precise definitions, and misunderstanding or misuse of these terms may
lead to errors and confusion in estimating energy available or making comparisons among fuels,
regions, or nations. This report describes the characteristics of fossil fuels that make it necessary
to use precise terminology, summarizes the major terms and their meanings, and provides a brief
summary of U.S. endowment of fossil fuels and the relationship between the U.S. fossil fuel
energy endowment and those of other nations.
Characteristics of Fossil Fuels
Fossil fuels are categorized, classified, and named using a number of variables. It is important to
keep in mind that naturally occurring deposits of any material, whether it is fossil fuels, gold or
timber, comprise a broad spectrum of concentration, quality, and accessibility (geologic,
technical, and cultural). These characteristics are graphically portrayed in Figure 1 as a resource
pyramid. At the top of the pyramid are the deposits that are high-quality, and easy to access.
These deposits have been generally discovered and produced first. Examples of the deposits at the
top of the resource pyramid are the large oil deposits of Saudi Arabia and the enormous natural
gas deposits of Qatar. Moving down the pyramid, the quality and/or accessibility declines, and
production becomes more difficult and expensive. A large oil deposit in the deep waters of the
Gulf of Mexico would be further down the pyramid than a comparable deposit on land because of
the added expense and technology required to produce it.
It is important to note that the deposits at the bottom of the pyramid may be quite extensive.
Deposits may be of poor quality or diffuse, but may occur in vast quantities. Examples of fossil
fuel deposits that would be found at the bottom of the pyramid are oil shale and methane hydrates
(both discussed further below). Oil shale and methane hydrate deposits contain massive amounts
of oil and natural gas, but their mode of occurrence, poor accessibility, and difficult recovery
make them sub-economic. The economic threshold for producing deposits further down the
pyramid is partly a function of commodity price. That threshold is also moved by the
development of new extraction technologies that make production feasible at lower cost.
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Figure 1. The Resource Pyramid Concept
All resources are not equal

Source: Michael Lardelli, “Earth as a Magic Pudding,” October 20, 2008, http://www.energybulletin.net/node/
46956, modified from Thomas Ahlbrandt and Peter J. McCabe, “Global Petroleum Resources: A View to the
Future,” Geotimes, November 2002, http://www.geotimes.org/nov02/feature_oil.html
For U.S. oil deposits, the resource pyramid (Figure 2) indicates that many of the high quality,
easy to find deposits have already been produced. Current proved reserves (terminology is
discussed below) include many deposits that are of lower quality or with poorer access than some
historical production, but which are still economic under current market conditions. As long as
demand for oil continues, the exploration and production process will move down the pyramid
under the influences of price (including environmental costs in some cases) and technology.
Whether the vast deposits of oil shale that are lower on the pyramid will be produced depends on
the price of oil, the cost of production (including environmental cost), and the availability of
technology to produce it. Although this example is for oil, similar relationships exist for natural
gas and coal.
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Figure 2. Resource Pyramid for U.S. Oil

Source: Historical production and proved reserves figures are from Energy Information Administration,
undiscovered technically recoverable resource value is from U.S. Geological Survey, and discovered and
undiscovered sub-economic resources uses the lower estimate for oil shale resources from RAND as a
minimum.
Notes: Discovered and undiscovered sub-economic resources would include poor quality or smal deposits of
conventional oil, some deposits of oil sands, and various other forms of oil deposits such as oil shale. Reserves
and Undiscovered Technical y Recoverable Resource numbers are for 2007 and 2008, respectively.
Terminology
A search for energy statistics in the literature quickly reveals a large number of terms used to
describe amounts of fossil fuels. Most of these terms have precise and legitimate definitions, and
even a careful comparison of statistics for diverse forms of fossil fuels can become quite difficult
to reconcile or understand. Not only do oil, natural gas, and coal occur in many diverse geologic
environments, but each commodity may occur in different modes or in different geologic settings
that impose vastly different economics on their recovery and delivery to market.
Examples of terms used for fossil fuel deposits (not an exhaustive list) include:
• Proved reserves
• Probable reserves
• Possible reserves
• Unproved reserves
• Demonstrated reserve base
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• Undiscovered resources
• Probable resources
• Possible resources
• Speculative resources
• Potential resources
• Technically recoverable resources
• Economically recoverable resources
Definitions for several of these terms are included in the Appendix.
Two particularly important distinctions afford a better understanding of fossil fuel statistics. The
first key distinction is between proved reserves and undiscovered resources; the second key
distinction is between conventional and unconventional deposits of fossil fuels.
Proved Reserves and Undiscovered Resources
For oil and natural gas, a major distinction in measuring quantities of energy commodities is
made between proved reserves and undiscovered resources. Understanding these terms will help
avoid confusion about statistical energy data.
Proved reserves are those amounts of oil, natural gas, or coal that have been discovered and
defined, typically by drilling wells or other exploratory measures, and which can be economically
recovered. In the United States, proved reserves are typically measured by private companies,
who report their findings to the Securities and Exchange Commission because they are
considered capital assets. Because proved reserves are defined by strict rules, they do not include
all of the oil or gas in a region, but only those amounts that have been carefully confirmed.1
Because proved reserves are, by definition, economically recoverable, the proportion of the oil in
the ground that qualifies as proved reserves grows when prices are high, and shrinks when prices
are low. That is, even without new discoveries, oil that may be sub-economic at $30 per barrel
becomes economic at $60 per barrel and so the total proved reserves increase simply because
price increases.
In addition to the volumes of proved reserves are deposits of oil and gas that have not yet been
discovered, and those are called undiscovered resources.2 The term “resource” has often been
used in a generic sense to refer to quantities of energy commodities in general. Observers may
refer to resource-rich nations, or speak about a large resource base, for example. But the term
“undiscovered resources” has a specific meaning. Undiscovered resources are amounts of oil and
gas estimated to exist in unexplored areas. Estimates of undiscovered resources for the United
States are made by the U.S. Geological Survey for resources on land, and by the U.S. Minerals

1 The Securities and Exchange Commission has recently modified their classification of reserves to include proved
reserves, probable reserves, and possible reserves, adding precision of language to the degree of certainty associated
with a particular volume of oil or gas, but also requiring increased attention to the terms used in energy statistics.
2 The historic question is “If they are undiscovered, how do we know they exist?” The answer is that there is a
probability that such deposits exist based on the geologic characteristics of a region, even if they have not been
discovered yet. The exploration process is predicated on the probability that such deposits exist.
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Management Service for resources offshore. These assessments are based on observation of
geological characteristics similar to producing areas and many other factors. Reported statistics
for undiscovered resources may vary greatly in precision and accuracy (determined
retrospectively), which are directly dependent upon data availability, and their quality may differ
for different fuels and different regions. Because estimates of undiscovered resources are based
partly on current production practices, they are generally reported as undiscovered technically
recoverable resources.
Another term sometimes used in the fossil fuels literature is “in-place” resources. In-place
resources are intended to represent all of the oil, natural gas, or coal contained in a formation or
basin without regard to technical or economic recoverability. Because only a small proportion of
the total amount of the fossil fuel in a deposit is ever recovered, there are large discrepancies
between technically recoverable resources and estimates of in-place resources. In-place resource
estimates sometimes result in very large numbers, which may be misleading if the reader does not
appreciate that the in-place volume of resource can never be completely produced or recovered.
The Importance of Terminology: The Example of the Bakken Formation
Research by a USGS geologist during the 1980s and 1990s revealed that a rock formation in the
Williston Basin of North Dakota, South Dakota, Montana, and southern Canada contained an
abundance of hydrocarbons dispersed throughout layers of shale and sandstone.3 Though the
author, Dr. Leigh Price, died before publishing his results, the numbers reported were quite
impressive: estimates of 271 to 503 billion barrels of oil attracted the attention of the oil industry.
However, those estimates, while huge, represented “in place” oil. That is, the total volume of oil
was huge, but it was disseminated throughout thousands of square miles of shale and only a small
portion of that total would be recoverable. At that time, production of unconventional (or
continuous) oil was not being done at large scales, so the technically recoverable volumes of oil
were modest.
Subsequently, the USGS has conducted a more detailed and thorough estimate of the technically
recoverable resources using modern directional drilling techniques and estimate that the Bakken
Formation contains 3.65 billion barrels of undiscovered technically recoverable oil and 1.85
trillion cubic feet (tcf) of undiscovered technically recoverable natural gas.4 These estimates are
still substantial in volume, and production in the Bakken Formation is proceeding. But the gap
between estimates of in-place oil and technically recoverable oil demonstrates vividly the
importance of knowing what the numbers represent.
Conventional Versus Unconventional Oil and
Natural Gas Deposits
The first oil and gas deposits discovered consisted of porous reservoirs in geologic formations,
capped by an impervious rock “trap” within which migrating fluids such as oil, natural gas, and

3 Leigh Price, Origins and Characteristics of the Basin-Centered Continuous Reservoir Unconventional Oil-Resource
Base of the Bakken Source System, Williston Basin, unpublished but available at http://www.undeerc.org/Price/.
4 Richard Pollastro, Assessment of Undiscovered Oil Resources in the Devonian-Mississippian Bakken Formation,
Williston Basin Province, Montana and North Dakota, 2008, U.S. Geological Survey Fact Sheet 2008-3021,
http://pubs.usgs.gov/fs/2008/3021/.
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water would accumulate. Within the reservoir, natural gas would be the least dense fluid and
would have accumulated at the top of the reservoir. Oil is more dense than gas, but less dense
than water and would pool in a layer below the gas cap. Below the oil and gas, water would fill
the confined reservoir. This layered arrangement of natural gas, oil, and water within a reservoir
is called a conventional deposit and has historically provided most of the oil and natural gas that
has been produced.
In recent decades, geologists began to realize that considerable volumes of oil and natural gas
exist outside conventional reservoirs in sedimentary rocks situated in geologic basins. The
distribution of oil or natural gas throughout a geologic formation over a wide area, but not in a
reservoir, is called an unconventional deposit (sometimes called a continuous deposit). The
amounts of oil and gas contained in unconventional deposits may be very large, but recovering
those deposits is sometimes difficult and expensive. An example of an unconventional oil deposit
is oil sand, in which the oil is distributed widely through the sandstone formation. Recovering the
oil from oil sands requires special technologies and treatments such as heating, steam flooding, or
even excavation. An example of an unconventional natural gas deposit is coalbed methane. The
natural gas (methane) does not exist in a discrete reservoir but is distributed throughout the pore
spaces of coal. When water is removed from the coal, the gas is released and can be produced.
Another type of unconventional natural gas deposit is shale gas, which is discussed below.
There is no direct correlation between the economic recoverability of a deposit and whether it is
conventional or unconventional. Some conventional deposits are not economically recoverable
because they are too small, too deep, or lack surface access. On the other hand, unconventional
deposits such as oil sands and coalbed methane are economically recoverable in some locations.
For example, coalbed methane production was 1.75 tcf in 20075 out of a total U.S. natural gas
production of 19.3 tcf (approximately 9%), and is an important component of U.S. natural gas
supply.
Authoritative Data Sources for U.S. Fossil Fuel
Reserves and Resources
Many individuals and institutions have attempted to compile and publish estimates of resources.
However, the statutory responsibility for collecting and publishing authoritative statistical
information on the various types of energy sources in the United States has been given to specific
Federal agencies. The Energy Information Administration (EIA) was originally created as the
Federal Energy Administration (FEA)6 and is charged with the responsibility of monitoring and
reporting U.S. energy reserves and production.
The Energy Information Administration (EIA) was created in response to the need for
additional Federal initiatives to collect and disseminate energy-related information, and to
evaluate and analyze this information. These needs were revealed as the United States sought
to respond to the energy crises of the 1970s. The first law to address these needs was the

5 http://tonto.eia.doe.gov/dnav/ng/xls/NG_ENR_CBM_A_EPG0_R52_BCF_A.xls
6 The Federal Energy Administration would later become the Energy Information Administration,
http://tonto.eia.doe.gov/abouteia/legislative_timeline.cfm.
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Federal Energy Administration Act of 1974 and, over the years, many subsequent laws have
contributed to EIA’s evolution and growth.
[The law] Created the FEA and mandated it to collect, assemble, evaluate, and analyze
energy information; provide energy information and projections to the Federal Government,
State Governments, and the public; and provide Congress with an annual report summarizing
these activities. It also provided FEA with data collection enforcement authority for
gathering data from energy producing and consuming firms.7
Likewise, the responsibility for assessing onshore undiscovered technically recoverable oil and
gas resources in the United States resides with the U.S. Geological Survey (USGS), in the
Department of the Interior.8 The USGS has conducted a number of national assessments of
undiscovered technically recoverable oil and natural gas resources over several decades. The most
recent complete national assessment for onshore oil and gas was completed in 1995, but USGS
updates that assessment on an ongoing basis as new data become available. Responsibility for
assessment of offshore undiscovered technically recoverable oil and gas resources belongs to the
Minerals Management Service, also within the Department of the Interior.9 EIA and USGS have
similar responsibilities for evaluating the nation’s endowment of coal.
In addition to purely governmental assessments, several expert groups provide perspectives on
individual fuels, geographic areas, or industry sector. Some of these groups are composed of
government, industry, and academic experts (e.g., the Potential Gas Committee10), expert
advisory committees for federal agencies (e.g., National Petroleum Council11), independent study
groups (e.g., the National Research Council, Committee on Earth Resources12), or professional
societies (e.g., American Association of Petroleum Geologists13 or the Society of Petroleum
Engineers14). Each of these groups provides considerable expertise to the assessment and
evaluation of oil and gas reserves and resources, and their reports are considered to be serious, but
none have the responsibility to provide a consistent, timely statistical review of U.S. oil and
natural gas resources. When using estimates generated by these expert groups, it is important to
look for clear and transparent explanation of assessment methodology; in the absence of
explanation, it will not be clear what is being estimated and the value and usefulness of the
statistics will be diminished.

7 1974: Federal Energy Administration (FEA) Act (P.L. 93-275, 15 USC 761)
8 http://energy.cr.usgs.gov/oilgas/noga/
9 http://www.mms.gov/offshore/
10 http://www.mines.edu/Potential-Gas-Committee-reports-unprecedented-increase-in-magnitude-of-U.S.-natural-gas-
resource-base
11 http://www.npc.org/
12 http://dels.nas.edu/besr/
13 http://www.aapg.org/
14 http://www.spe.org/spe-app/spe/index.jsp
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U.S. Oil and Natural Gas Reserves and Resources
Proved Reserves
U.S. proved reserves of oil as reported by EIA total 21.317 billion barrels.15 The data are from the
latest full compilation, at the end of calendar year 2007. There is generally a delay of over a year
between the end of a reporting year and the compilation of the data because the process is time-
consuming and quality control is essential. The EIA value for proved reserves includes both
onshore and offshore reserves.
Compiling oil reserves is not a simple arithmetic exercise. Each year, volumes of individual
components change significantly. Below is a list of how the reserves changed during 2007 as a
function of the normal exploration, production, and business processes conducted by oil
companies. A more detailed description of these terms is in the Appendix.
• Adjustments (+,-) 65 million barrels
• Revision Increases (+) 2,278 million barrels
• Revision Decreases (-) 1,078 million barrels
• Sales (-) 811 million barrels
• Acquisitions (+) 792 million barrels
• Extensions (+) 651 million barrels
• New Field Discoveries (+) 66 million barrels
• New Reservoir Discoveries in Old Fields (+) 73 million barrels
• Estimated Production (-) 1,691 million barrels
U.S. proved reserves of natural gas, also reported by EIA for 2007 total 237.726 tcf.16 Like oil,
the compilation of proved reserves of natural gas involved keeping track of several kinds of
production and adjustments. The liquid components (natural gas liquids) are reported with oil
production.17 Total proved reserves are reported as dry natural gas and includes both onshore and
offshore reserves. The following list shows a breakdown of how natural gas production is
reported prior to separation into its gas and liquid components.
• Natural Gas, Wet After Lease Separation 247.789 tcf
• Natural Gas Nonassociated, Wet After Lease Separation 215.121 tcf
• Natural Gas Associated-Dissolved, Wet After Lease Separation 32.668 tcf
• Natural Gas Liquids (Million Barrels) 9.143

15 Energy Information Administration, Data as of 12/31/2007, Release Date: 2/10/2009, http://tonto.eia.doe.gov/dnav/
pet/pet_crd_pres_dcu_NUS_a.htm
16 Energy Information Administration, Data as of 12/31/2007, Release Date: 2/10/2009, http://tonto.eia.doe.gov/dnav/
ng/ng_enr_sum_dcu_NUS_a.htm
17 http://tonto.eia.doe.gov/cfapps/ipdbproject/docs/IPMNotes.html#p1
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Undiscovered Oil and Natural Gas Resources
As mentioned previously, the responsibility for assessing the undiscovered technically
recoverable resources of oil and natural gas is split between the USGS for onshore resources, and
the MMS for offshore resources. USGS and MMS use somewhat different assessment
methodologies. The combined results of the onshore and offshore assessments are based on the
availability of geologic data, which may be quite limited, especially for certain offshore areas.
Nevertheless, the estimates are complementary and are tabulated in Tables 1 and 2. The USGS
distinguishes between conventional and unconventional undiscovered resources and they are
reported separately for oil, natural gas, and natural gas liquids. MMS reports their estimates for
each offshore planning region but does not distinguish between conventional and unconventional
deposits.
Table 1.Onshore U.S. Oil, Natural Gas, and Natural Gas Liquids
Undiscovered Technically Recoverable Resources (UTRR)
Oil
Natural Gas
Natural Gas Liquids

(Bbo)
(Tcf)
(BOE)
Conventional
41.38
378.60
7.38
Unconventional (continuous)
6.16
364.20
4.77
TOTAL U.S. ONSHORE UTRR
47.53
742.88
12.11
Source: U.S. Geological Survey, Department of the Interior, 2008: http://certmapper.cr.usgs.gov/data/noga00/
natl/tabular/2008/summary_08.pdf.
Notes: Unconventional natural gas includes coalbed methane; Bbo = billion barrels of oil, Tcf = trillion cubic
feet, BOE = billion barrels of oil equivalent.
Table 2.Offshore U.S. Oil and Natural Gas
Undiscovered Technically Recoverable Resources (UTRR), mean values
Oil
Natural Gas
U.S. OCS Region
(Bbo)
(Tcf)
Alaska
26.6
132.0
Atlantic
3.8
36.9
Gulf of Mexico
44.9
232.5
Pacific
10.5
18.2
TOTAL U.S. OFFSHORE UTRR
85.8
419.8
Source: Minerals Management Service, Department of the Interior, 2006: http://www.mms.gov/revaldiv/PDFs/
2006NationalAssessmentBrochure.pdf
Notes: Bbo = billion barrels of oil; Tcf = trillion cubic feet; BOE = billion barrels of oil equivalent
The total endowment of technically recoverable oil and natural gas for the United States is
obtained by summing proved reserves from EIA with the onshore and offshore undiscovered
technically recoverable resources from USGS and MMS, as shown in Table 3.
The value for total technically recoverable natural gas (1,400.49 tcf) does not include much of the
newly prospective shale gas being explored in the United States. According to a 2009 report by
the Potential Gas Committee, a consortium of industry, academic, and government experts, the
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total “future supply” of natural gas is 2,074 tcf, which includes substantial volumes of shale gas
(see description of shale gas below).
Table 3.Total U.S. Endowment of Technically Recoverable Oil and Natural Gas
(sum of EIA reserves, USGS, and MMS UTRR values)
Oil
Natural Gas

(Bbo)
(Tcf)
Total U.S. UTRR
145.5a 1,162.7
Proved reserves
21.3
237.7
Total U.S. endowment
166.7
1,400.4
Note: Bbo = billion barrels of oil, Tcf = trillion cubic feet.
a. Represents the total of technical y recoverable oil plus natural gas liquids from Tables1 and 2.
Sub-Economic18 Oil and Natural Gas Resources
Shale Oil
After coal, shale oil represents the most abundant fossil fuel in the United States. However,
despite government programs in the 1970s and early 1980s to stimulate development of the
resource, production of shale oil is not yet commercially viable. The need for massive capital
investment and the cost of production itself have been the major barriers. A further economic
factor lies in the fact that shale oil has a unique chemical composition and, unlike conventional
crude oil, cannot be distilled to produce gasoline, but would be primarily a source of other liquid
middle distillate fuels such as jet fuel or diesel oil, fuels for which there is significant national
demand.
In addition, production of shale oil requires large amounts of water, an important factor since
most of the resource is located in water-scarce regions of western Colorado, Utah, and Wyoming.
Other environmental problems include the difficulty in disposing of tailings if excavation is used
as the extraction process, and the production of greenhouse gases.
In light of these difficulties, efforts to aid in the development of shale oil are focused on pilot
projects to test alternative technologies of production.19
Estimates of the amount of hydrocarbon fuel in U.S. shale oil resources are highly speculative,
given the small amount of development that has taken place. The Department of Energy (DOE)
Office of Naval Petroleum and Oil Shale estimates that approximately 1.38 trillion barrels of
shale oil are potentially recoverable from the roughly 7.8 million acres of federal oil shale.20 A

18 The amount of resources considered “sub-economic” changes with economic conditions and extraction technologies.
19 For more details about shale oil development, see CRS Report RL34748, Developments in Oil Shale, by Anthony
Andrews1.
20 U.S. DOE, Office of Petroleum and Oil Shale Reserves, National Strategic Unconventional Resource Model, April
2006.
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more conservative estimate by the RAND Corporation is that 800 billion barrels may be
recoverable.21
Shale Gas
Shale gas is an emerging type of natural gas deposit, and exploration for and production of shale
gas is increasing. Shale gas is currently marginally economic, and production is therefore
sensitive to the price of natural gas; if natural gas prices increase, production of shale gas would
likely increase. Shale gas is a classical unconventional type of deposit; the gas is distributed
throughout the low permeability shale formations rather than accumulating in a more permeable
reservoir. The occurrence of gas in this manner requires special production techniques that often
involve horizontal drilling into the gas-bearing formation, followed by hydrofracturing of the
rock (exerting pressure in the gas well so high that it causes brittle rock to fracture) to release the
gas from the rock. The use of hydrofracturing has caused some environmental concerns arising
from the injection of large amounts of water into the well, concerns about the chemical
composition of the injected fluids, fears that the fractured rock will expose local water wells to
non-potable waters, and the observation that some hydrofracturing jobs have apparently created
small earthquakes. However, industry officials insist that any environmental concerns could be
mitigated through careful production practices.
No systematic assessment of shale gas resources has been conducted for the United States, though
industry and academic experts estimate that the technically recoverable volumes of natural gas
from these shale deposits are very large. Recently, the Potential Gas Committee estimated that the
United States has 616 tcf of “potential natural gas resources” occurring as shale gas.22 The
proportion of that resource that will actually be produced will depend on further development of
exploration and production technology, the price of natural gas, and the ways in which states deal
with potential environmental issues.
Methane Hydrates
Another form of fossil fuel with potentially vast resources is natural gas in the form of methane
hydrate. Methane hydrate (sometimes called natural gas hydrate, or just gas hydrates) are being
investigated as an energy source by both DOE23 and USGS.24 Methane hydrate is a crystalline
solid composed of methane and water which forms in porous rocks under very specific conditions
of temperature and pressure. Deposits occur most commonly offshore in the sediments or rocks of
the continental shelf and slope, or in cold climates such as northern Alaska and Canada. Although
considered a scientific oddity until the 1990s, methane hydrates are now known to exist in
hundreds of locations around the world, often in small isolated deposits, but sometimes in
massive quantities. Total worldwide in-place resources of methane hydrates are probably huge,
perhaps thousands of trillion cubic feet, but hydrates have never been produced commercially.
Currently efforts by the United States, Canada, Japan, India, and several other nations are aimed
at developing technologies to exploit this large and widespread form of natural gas.

21 J. T. Bartis, T. LaTourrette, L. Dixon, D.J. Peterson, and G. Cecchine, Oil Shale Development in the United States
Prospects and Policy Issues (MG-414-NETL), RAND Corporation, 2005.
22 http://geology.mines.edu/pgc/index.html
23 http://www.fossil.energy.gov/programs/oilgas/hydrates/
24 http://energy.usgs.gov/other/gashydrates/
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The mean in-place gas hydrate resource for the entire United States is estimated to be 320,000 tcf
of gas, with approximately half of this resource occurring offshore of Alaska and most of the
remainder occurring beneath the continental margins of the lower 48 states.25 The USGS
estimates that there are about 85 tcf of undiscovered, technically recoverable gas resources within
gas hydrates in northern Alaska, and recent studies have shown that methane hydrates are more
abundant in the sediments of the Gulf of Mexico than previously believed.26 Improved
understanding of the occurrence and behavior of these important natural gas deposits, and
improved technology for producing them, may make methane hydrates a viable source of natural
gas in the future.
Heavy Oil
Heavy oil, so-named because its specific gravity and viscosity are higher than those of light crude
oil, constitutes substantial deposits of oil in Canada, Venezuela, and other parts of the world.
Canada’s Athabasca oil sands and Venezuela’s Orinoco oil sands are the largest deposits of this
type. Canada’s oil sands contain an estimated 173 billion barrels of technically recoverable oil
and accounts for more than half of Canada’s oil production. The Orinoco oil sands are estimated
to contain 1.36 trillion barrels of extra heavy oil in-place, of which approximately 270 billion
barrels are technically recoverable.27 Oil sands generally require special production techniques
such as excavation or steam flooding, and the oil produced is often limited to certain refineries
equipped to handle the heavy oil. U.S. heavy oil is found in California, Alaska, and Wyoming,
and is estimated to constitute in-place resources of up to 100 billion barrels of oil, though
production of heavy oil in the United States is declining because of the depth of the resource and
the cost of production.28

25 Statement of Dr. Timothy S. Collett, Research Geologist, U.S. Geological Survey, U.S. Department of the Interior,
Before the House Committee on Resources Subcommittee on Energy and Mineral Resources: On Unconventional Fuels
II: The Promise of Methane Hydrates, July 30, 2009.
26 http://www.usgs.gov/newsroom/article.asp?ID=2227
27 http://www.eia.doe.gov/oiaf/aeo/otheranalysis/aeo_2006analysispapers/nlf.html
28 http://fossil.energy.gov/programs/reserves/npr/Heavy_Oil_Fact_Sheet.pdf
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U.S. Coal Reserves and Resources
EIA is the authoritative source for coal reserves and resource estimates for the United States. EIA
compiles data on coal reserves and resources from state sources and federal sources, including
from work done by the USGS.29 The terminology used for coal is slightly different than for oil
and natural gas. The primary statistic reported by EIA is the demonstrated reserve base (DRB),
which is comprised of coal resources that have been identified to specified levels of accuracy and
may support economic mining under current technologies.30 For the latest reporting period,
calendar year 2007, the U.S. demonstrated reserve base was 489 billion short tons.31 Because the
United States produces and consumes about 1.2 billion short tons of coal per year, the
demonstrated reserve base would appear to provide hundreds of years’ supply of coal, if U.S.
users continue to consume it at the same rate. However, because coal production often requires
ground disturbance, especially for open-pit mining, the amount that is technically recoverable is
not always available. EIA has applied an availability factor that reduces the technically
recoverable amount to 262 billion short tons that would actually be available for mining.32
Detailed availability studies by the USGS have indicated that, at least in some cases, the available
and economically recoverable coal might be even substantially less than the technically
recoverable amount:33
... a significant portion of the coal resources less than 4,000 ft (1,219.2 m) in depth are also
typically subeconomic due to a number of restrictions that further limit their availability and
recoverability. Some of these restrictions are technical constraints (using existing
technology) such as coal beds too thin to recover or dipping too steeply. Many societal or
environmental restrictions such as the presence of towns, wetlands, or other environmentally
sensitive areas may also preclude coal recovery. Both regional mine planning and economic
studies are necessary to derive estimates of the coal reserves for any given area.
For example, in one specific case in Wyoming, 47% of the in-place coal is technically
recoverable, but the available, economically recoverable coal is only about 6% of the in-place
coal.34 While these proportions may vary between 5% and 20%, depending upon the specific
conditions for each coal mining area, very large coal numbers are viewed with some caution
because in-place numbers, or even recoverable numbers, may not provide a realistic assessment
of the coal that could actually be produced.

29 http://energy.cr.usgs.gov/coal/coal_assessments/summary.html
30 http://www.eia.doe.gov/cneaf/coal/reserves/reserves.html
31 A short ton is 2,000 pounds. A metric tonne is 2,204 pounds.
32 http://www.eia.doe.gov/cneaf/coal/reserves/reserves.html
33 James A. Luppens, Timothy J. Rohrbacher, Lee M. Osmonson, and M. Devereux Carter, Coal
Resource Availability, Recoverability, and Economic Evaluations in the United States—A
Summary, U.S. Geological Survey Professional Paper 1625-F, Chapter D, 2009.
34 http://pubs.usgs.gov/of/2008/1202/pdf/ofr2008-1202.pdf
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Expressing Fossil Fuels as Barrels of Oil Equivalent
(BOE)
It is sometimes useful to equate the different types of fossil fuels in order to compare the energy
content or to gauge the magnitude of one type of fossil fuel in terms of another. Fossil fuels may
be liquid, gas, and solid; oil is a liquid measured in barrels, natural gas is a gas measured in cubic
feet, coal is a solid measured in pounds or short tons, and all three types of fossil fuels vary in
composition, quality, and heat content. Therefore, converting one type of fossil fuel to an
equivalent amount of another is a slightly problematic calculation. For example, the energy
content of coal varies by at least a factor of three depending on grade.35 However, government
and industry sources commonly use rule-of-thumb measures to make these conversions. For
example, EIA provides a conversion tool on their website36 that assumes the following heat
contents (based on U.S. consumption, 2008):

Coal
1 Short Ton = 19,988,000 Btu37
Natural gas
1 Cubic Foot = 1,028 Btu
Oil
1 Barrel = 42 U.S. gal ons = 5,800,000 Btu

Using these rule-of-thumb heat values, we can express natural gas and coal units in terms of
barrels of oil equivalent (BOE):

Coal
1 Short Ton = 3.45 BOE
Natural gas
1 million cubic feet = 1,028,000,000 Btu = 177.2 BOE = 5,643 cubic feet/barrel

Using these conversion factors, we present a crude comparison of U.S. energy reserves plus
resources in Table 4.
Table 4.U.S. fossil fuel reserves and resources expressed as BOE
BOE = Barrels of oil equivalent
Fossil Fuel
Native units
BOE
Technical y recoverable oila 166.7
billion barrels 166.7
billion BOE
Technically recoverable natural gas
1,400.4 trillion cubic feet
248.2 billion BOE
Recoverable reserve base of coal
262 billion short tons
903.9 billion BOE
TOTAL U.S. fossil fuel endowment
1,318.8 billion BOE
a. Technical y recoverable oil and natural gas includes proved reserves plus undiscovered technical y
recoverable resources.

35 http://www.aps.org/policy/reports/popa-reports/energy/units.cfm
36 http://tonto.eia.doe.gov/kids/energy.cfm?page=about_energy_conversion_calculator-basics
37 Btu is the abbreviation for British thermal units, a common measure of heat content. One Btu is the amount of energy
in the form of heat required to raise the temperature of one pound of water one degree Fahrenheit.
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A Brief Overview of Global Fossil Fuel Resources
Reliable values for proved reserves and undiscovered resources outside the United States are less
available than for the United States. The only source of data for some countries is one of the
nation’s ministries (energy, resource, interior, commerce, etc.), and those data may not be
completely accurate because of the lack of good geologic data and assessment methodology, or
because the information is purposely withheld. In fact, even if all nations wished to report their
resource estimates reliably, it would not be possible to collect uniform data because different
methods, accounting rules, and terminology are used in each country. Therefore, some reserve
statistics reported outside the United States are not consistent with the U.S. data. Furthermore,
only reserves and production statistics are reported for most nations. There has been no reliable
source for estimates of undiscovered oil and natural gas resources internationally since the U.S.
Geological Survey completed its World Petroleum Assessment in 2000.38
Data for proved reserves and production in all countries are most reliable. Production statistics
can be obtained for the Organization of the Petroleum Exporting Countries (OPEC)39 and for the
Organization for Economic Cooperation and Development (OECD) countries from the
International Energy Agency,40 an arm of OECD. For international statistics, the EIA relies on the
Oil & Gas Journal (a publication of PennWell Corporation) or World Oil (a publication of Gulf
Publishing Company) for foreign oil and natural gas reserves. These energy industry trade
publications monitor individual national sources for information, as described by the Oil & Gas
Journal:
OGJ does not make its own estimates of a country’s reserves but rather compiles the
estimates of proved reserves from an annual survey of official sources, including government
agencies and ministries. Since most countries do not assess their reserves annually, many of
the figures in this report are unchanged from a year ago.41
World Oil summarizes their data sources this way:
World Oil’s tables are produced with data from a variety of sources, including governmental
agencies. Operating companies with drilling programs also contributed to this year’s survey.
Our survey is not scientifically randomized, and new environmental and political challenges
may emerge at any time. In some cases, a country may not have responded to our surveys, in
which case we might use proxies such as rig counts and third-party sources, both public and
private.42
A source of global oil and gas information commonly used by a number of analysts is the BP
Statistical Review of World Energy.43 Some of BP’s data also comes from Oil & Gas Journal and
World Oil, but is supplemented with additional data:

38 U.S. Geological Survey, World Petroleum Assessment, 2000, http://certmapper.cr.usgs.gov/rooms/we/index.jsp.
39 http://www.opec.org/home/.
40 http://www.iea.org/index.asp.
41 Marilyn Radler, Oil & Gas Journal, “New estimates boost worldwide oil, gas reserves,” December 22, 2008.
42 World Oil, Production and reserves lag as world drilling grows, September, 2008.
43 http://www.bp.com/productlanding.do?categoryId=6929&contentId=7044622.
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The reserve numbers published in the BP Statistical Review of World Energy are an estimate
of proved reserves, drawn from a variety of official primary sources and data provided by the
OPEC Secretariat, Cedigaz, World Oil and the Oil & Gas Journal and an independent
estimate of Russian oil reserves based on information in the public domain. Oil reserves
include field condensate and natural gas liquids as well as crude oil. They also include an
estimate of Canadian oil sands ‘under active development’ as a proxy for proved reserves.
This inclusive approach helps to develop consistency with the oil production numbers
published in the Review, which also include these categories of oil.
The BP Statistical Review of World Energy uses data from the World Energy Council (WEC)44
for coal reserves. The WEC is a global consortium of national committees that compile energy
statistics for their own countries. WEC estimates for oil and natural gas reserves differ somewhat
from the Oil & Gas Journal and World Oil values, but not dramatically. For the United States, the
U.S. Energy Association (USEA)45 is the WEC national committee, and USEA cites EIA sources
for its estimates for the United States. When using any international fossil fuel statistics, users
should be cognizant of ultimate sources of data among these energy data organizations.
Using the best-available data, it is possible to draw a comparison of the total endowment of fossil
fuels for nations. Table 5 includes the basic data for oil, natural gas, and coal for selected nations,
with calculations of the total fossil fuels in each nation, expressed in billions of barrels of oil
equivalent (billion BOE).

44 http://www.worldenergy.org/
45 http://www.usea.org/
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Table 5.Total Fossil Fuel Reserves of Selected Nations
(expressed in native units and as billions of barrels of oil equivalent (BOE))
Natural
Natural
Coal
Oil
Gas
Gas As
As
Total Fossil

Reservesa
Reserves
BOE Coal
BOE
Fuels in BOE
(billions of
(trillion
(billion
(billions of

barrels)
cubic feet)

short tons)

barrels)
World 1,332.0
6,212.3
1,100.8
929.3
3,206.1
5,638.9
Saudi Arabia
266.8
253.1
44.8
0.0
0.0
311.6
Canada 178.6
58.2
10.3
7.3
25.2
214.1
Iran 138.4
948.2
168.0
1.5
5.2
311.6
Iraq 115.0
111.9
19.8
0.0
0.0
134.8
Kuwait 104.0
56.0
9.9
0.0
0.0
113.9
United Arab Emirates
97.8
214.4
38.0
0.0
0.0
135.8
Venezuela 87.0
166.3
29.5
0.5
1.8
118.3
Russia
60.0
1,680.0
297.7
173.1
597.2
954.9
Libya 41.5
54.4
9.6
0.0
0.0
51.1
Nigeria 36.2
184.0
32.6
0.2
0.7
69.5
Kazakhstan 30.0
100.0
17.7
34.5
119.0
166.7
United States
21.3
237.7
42.1
262.7
906.3
969.7
China 16.0
80.0
14.2
126.2
435.4
465.6
Qatar 15.2
905.3
160.4
0.0
0.0
175.6
Brazil 12.2
12.9
2.3
7.8
26.9
41.4
Algeria 12.2
159.0
28.2
0.1
0.2
40.6
Mexico 11.7
13.2
2.3
1.3
4.5
18.5
Angola 9.0
9.5
1.7
0.0
0.0
10.7
Azerbaijan 7.0
30.0
5.3
0.0
0.0
12.3
Norway 6.9
79.1
14.0
0.0
0.0
20.9
Turkmenistan 0.6
100.0
17.7
0.0
0.0
18.3
Indonesia 4.0
106.0
18.8
4.8
16.5
39.2
Malaysia 4.0
83.0
14.7
0.0
0.0
18.7
Uzbekistan 0.6
65.0
11.5
3.3
11.4
23.5
Egypt 3.7
58.5
10.4
0.0
0.1
14.1
Australia and New Zealand
1.6
31.2
5.5
85.1
293.6
300.7
India 5.6
38.0
6.7
62.3
214.9
227.3
Source: Energy Information Administration, http://www.eia.doe.gov/emeu/international/contents.html.
Note: All values are for 2007 or latest available data. Countries are listed in order of oil reserve ranking.
a. Oil and natural gas reserve numbers are from the EIA tables, using only the Oil & Gas Journal values.
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Using only proved reserve numbers for the United States and other nations shows that the United
States remains among the top nations in proved reserves of all fossil fuels taken together.
Values for technically recoverable oil and natural gas resources estimated by the USGS contain
greater uncertainty than the statistics for proved reserves. Nevertheless, adding the estimates for
undiscovered technically recoverable oil and natural gas provides a more inclusive estimate of
total endowment of technically recoverable fossil fuels. Table 6 adds technically recoverable oil
and natural gas resources to the proved reserve figures of Table 5 to provide a more complete
tabulation of technically recoverable fossil fuels. Values for total fossil fuels in Table 6 include
the estimates for coal reserves in the first column but do not include any estimates for
undiscovered coal resources; those data simply do not exist in any consistent form for various
nations.
As an example of how such undiscovered coal resources might affect the ultimate total
endowment of fossil fuels, the U.S. coal resource estimates do not include some potentially
massive deposits of coal that exist in northwestern Alaska. These currently inaccessible coal
deposits have been estimated to be more than 3,200 billion short tons of coal.46 Only a portion of
that coal would likely be technically recoverable even if development were pursued but,
nevertheless, it suggests other fossil fuel deposits in many parts of the world that have not been
estimated or are not available for extraction.

46 Romeo M. Flores, Gary D. Stricker, and Scott A. Kinney, “Alaska Coal Resources and Coalbed Methane Potential,”
U.S. Geological Survey Bulletin 2198, 2003.
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U.S. Fossil Fuel Resources: Terminology, Reporting, and Summary

Table 6. Reserves of Fossil Fuels Plus Technically Recoverable Undiscovered Oil and
Natural Gas
Estimated
Total Fossil Fuel
Undiscovered Oil
Proved Reserves
and Gas
Total Fossil Fuelsb

(from Table 5)
(Billion BOE, USGSa)
(Billion BOE)
Saudi Arabia
311.6
231.3
543.0
Canada 214.1
7.2
221.3
Iran 311.6
114.3
425.9
Iraq 134.8
68.4
203.3
Kuwait 113.9
4.7
118.6
United Arab Emirates
135.8
16.2
152.0
Venezuela 118.3
38.1
156.4
Russia
954.9
293.7
1,248.6
Libya 51.1
10.8
61.9
Nigeria 69.5
63.4
133.0
Kazakhstan 166.7
33.7
200.4
United States
969.7
351.5
1,321.3
China 465.6
28.4
494.0
Qatar 175.6
12.1
187.7
Brazil 41.4
79.4
120.8
a. U.S. Geological Survey, World Petroleum Assessment, 2000, http://energy.cr.usgs.gov/WEcont/WEMap.pdf;
mean values of estimates are used for foreign countries. U.S. number is taken from values in Table 3.
b. Total Fossil Fuels in this table include the technically recoverable reserves of oil, natural gas, and coal from
Table 5, plus estimates of undiscovered oil and natural gas from the USGS World Petroleum Assessment.
No global estimates of undiscovered coal exist.
A meaningful comparison of the ultimate endowments of fossil fuels among nations would
include the important deposits of oil, natural gas, and coal that are lower on the resource pyramid
in Figure 1, and that might be exploited in the future given the appropriate technology, economic
viability, and environmental acceptability. However, the uncertainty associated with estimates of
those deposits is too great to produce meaningful comparisons. For example, the values in Table
6 could be amended further by including estimates of oil shale or methane hydrate resources, but
the final tally would have very little meaning considering the difficulties in estimating those
resources. The United States has considerable amounts of fossil fuels, both conventional and
unconventional, both discovered and undiscovered, that are not currently economically viable.
However, it is likely that other nations contain similar deposits but lack any comprehensive
assessment of those resources.
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U.S. Fossil Fuel Resources: Terminology, Reporting, and Summary

U.S. Production and Consumption of Oil,
Natural Gas, and Coal
To provide some scale for the reserves and undiscovered resource values reported above, Table 7
lists production and consumption of oil, natural gas, and coal by the United States. For a more
complete summary of U.S. energy supply and demand, see CRS Report R40187, U.S. Energy:
Overview and Key Statistics, by Carl E. Behrens and Carol Glover.
Table 7.United States Annual Consumption of Oil, Natural Gas, and Coal
Values are for year-end, 2008
Production
Consumption
Oil
2.46 billion barrels/year (2.46 billion BOE)
7.1 billion barrels/year (7.1 billion BOE)
Natural Gas
20.6 trillion cubic feet/year (3.7 billion BOE)
23.2 trillion cubic feet/year (4.1 billion BOE)
Coal
1.17 billion short tons/year (4.0 billion BOE)
1.04 billion short tons/year (3.6 billon BOE)
Source: Energy Information Administration, http://www.eia.doe.gov/.
Notes: Natural gas is reported on a dry basis, BOE = barrels of oil equivalent.

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Appendix. Definition of Terms
Reserves and Resources Terms
Definitions of terms taken from U.S. Department of the Interior, Survey of Available Data on
OCS Resources and Identification of Data Gaps, Report to the Secretary, OCS Report MMS
2009-015, Appendix A, List of Terms Used, http://www.doi.gov/ocs/report.pdf.
Proved reserves. The quantities of hydrocarbons estimated with reasonable certainty to be
commercially recoverable from known accumulations under current economic conditions,
operating methods, and government regulations. Current economic conditions include prices and
costs prevailing at the time of the estimate. Estimates of proved reserves do not include reserves
appreciation.
Reserves. The quantities of hydrocarbon resources anticipated to be recovered from known
accumulations from a given date forward. All reserve estimates involve some degree of
uncertainty.
Reserves appreciation. The observed incremental increase through time in the estimates of
reserves (proved and unproved) of an oil and/or natural gas field as a consequence of extension,
revision, improved recovery, and the additions of new reservoirs.
Resources. Concentrations in the earth’s crust of naturally occurring liquid or gaseous
hydrocarbons that can conceivably be discovered and recovered.
Undiscovered resources. Resources postulated, on the basis of the geologic knowledge and
theory, to exist outside of known fields or accumulations.
Undiscovered technically recoverable resources (UTRR). Oil and gas that may be produced as
a consequence of natural pressure, artificial lift, pressure maintenance, or other secondary
recovery methods, but without any consideration of economic viability. They are primarily
located outside of known fields.
Undiscovered economically recoverable resources (UERR). The portion of the undiscovered
technically recoverable resources that is economically recoverable under imposed economic and
technologic conditions.
Unproved reserves. Quantities of hydrocarbon resources that are assessed based on geologic and
engineering information similar to that used in developing estimates of proved reserves, but
technical, contractual, economic, or regulatory uncertainty precludes such reserves from being
classified as proved.
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Key Terms Used in Oil Statistics

Acquisitions
The volume of proved reserves gained by the purchase of existing fields or properties, from the date
of purchase or transfer.
Adjustments
The quantity which preserves an exact annual reserves balance within each State or State subdivision
of the following form:

Adjustments + Revision Increases - Revision Decreases - Sales + Acquisitions + Extensions + New
Field Discoveries + New Reservoir Discoveries in Old Fields - Report Year Production = Published
Proved Reserves at End of Report Year

These adjustments are the yearly changes in the published reserve estimates that cannot be
attributed to the estimates for other reserve change categories because of the survey and statistical
estimation methods employed. For example, variations as a result of changes in the operator frame,
different random samples or imputations for missing or unreported reserve changes, could
contribute to adjustments.
Crude Oil
A mixture of hydrocarbons that exists in the liquid phase in natural underground reservoirs and
remains liquid at atmospheric pressure after passing through surface separating facilities. Crude oil
may also include:
Small amounts of hydrocarbons that exist in the gaseous phase in natural underground reservoirs but
are liquid at atmospheric pressure after being recovered from oil well (casinghead) gas in lease
separators, and that subsequently are comingled with the crude stream without being separately
measured.
Small amounts of non-hydrocarbons produced with the oil.
When a State regulatory agency specifies a definition of crude oil which differs from that set forth
above, the State definition is to be fol owed.
Extensions
The reserves credited to a reservoir because of enlargement of its proved area. Normally the
ultimate size of newly discovered fields, or newly discovered reservoirs in old fields, is determined by
wells drilled in years subsequent to discovery. When such wells add to the proved area of a
previously discovered reservoir, the increase in proved reserves is classified as an extension.
New Field
The volumes of proved reserves of crude oil, natural gas and/or natural gas liquids discovered in new
Discoveries
fields during the report year.
New Reservoir
The volumes of proved reserves of crude oil, natural gas, and/or natural gas liquids discovered during
Discoveries in
the report year in new reservoir(s) located in old fields.
Old Fields
Production,
The volumes of crude oil which are extracted from oil reservoirs during the report year. These
Crude Oil
volumes are determined through measurement of the volumes delivered from lease storage tanks,
(i.e., at the point of custody transfer) with adjustment for (1) net differences between opening and
closing lease inventories, and for (2) basic sediment and water. Oil used on the lease is considered
production.
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Proved Reserves
Proved reserves of crude oil as of December 31 of the report year are the estimated quantities of all
of Crude Oil
liquids defined as crude oil, which geological and engineering data demonstrate with reasonable
certainty to be recoverable in future years from known reservoirs under existing economic and
operating conditions.

Reservoirs are considered proved if economic producibility is supported by actual production or
conclusive formation test (drill stem or wire line), or if economic producibility is supported by core
analyses and/or electric or other log interpretations. The area of an oil reservoir considered proved
includes: (1) that portion delineated by drilling and defined by gas—oil and/or gas—water contacts, if
any; and (2) the immediately adjoining portions not yet drilled, but which can be reasonably judged as
economically productive on the basis of available geological and engineering data. In the absence of
information on fluid contacts, the lowest known structural occurrence of hydrocarbons is
considered to be the lower proved limit of the reservoir.

Volumes of crude oil placed in underground storage are not to be considered proved reserves.

Reserves of crude oil which can be produced economically through application of improved recovery
techniques (such as fluid injection) are included in the “proved” classification when successful testing
by a pilot project, or the operation of an installed program in the reservoir, provides support for the
engineering analysis on which the project or program was based.

Estimates of proved crude oil reserves do not include the following: (1) oil that may become available
from known reservoirs but is reported separately as “indicated additional reserves”; (2) natural gas
liquids (including lease condensate); (3) oil, the recovery of which is subject to reasonable doubt
because of uncertainty as to geology, reservoir characteristics, or economic factors; (4) oil that may
occur in undrilled prospects; and (5) oil that may be recovered from oil shales, coal, gilsonite, and
other such sources. It is necessary that production, gathering or transportation facilities be installed
or operative for a reservoir to be considered proved.
Revisions
Changes to prior year-end proved reserves estimates, either positive or negative, resulting from new
information other than an increase in proved acreage (extension). Revisions include increases of
proved reserves associated with the instal ation of improved recovery techniques or equipment.
They also include correction of prior report year arithmetical or clerical errors and adjustments to
prior year-end production volumes to the extent that these alter reported prior year reserves
estimates.
Sales
The volume of proved reserves deducted from an operator’s total reserves when selling an existing
field or property, during the calendar year.
Source: EIA, http://tonto.eia.doe.gov/dnav/pet/TblDefs/pet_crd_pres_tbldef2.asp.
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Key Terms Used in Natural Gas Statistics

Dry Natural Gas
Natural gas which remains after: (1) the liquefiable hydrocarbon portion has been
removed from the gas stream (i.e., gas after lease, field, and/or plant separation); and
(2) any volumes of non-hydrocarbon gases have been removed where they occur in
sufficient quantity to render the gas unmarketable. (Note: Dry natural gas is also
known as consumer-grade natural gas. The parameters for measurement are cubic feet
at 60 degrees Fahrenheit and 14.73 pounds per square inch absolute.)
Natural Gas Associated-
The combined volume of natural gas which occurs in crude oil reservoirs either as free
Dissolved
gas (associated) or as gas in solution with crude oil (dissolved).
Natural Gas Liquids
Those hydrocarbons in natural gas which are separated from the gas through the
processes of absorption, condensation, adsorption, or other methods in gas processing
or cycling plants. General y such liquids consist of propane and heavier hydrocarbons
and are commonly referred to as condensate, natural gasoline, or liquefied petroleum
gases. Where hydrocarbon components lighter than propane are recovered as liquids,
these components are included with natural gas liquids.
Natural Gas Non-associated
Natural gas not in contact with significant quantities of crude oil in a reservoir.
Natural Gas, Wet After
The volume of natural gas remaining after removal of lease condensate in lease and/or
Lease Separation
field separation facilities, if any, and after exclusion of non-hydrocarbon gases where
they occur in sufficient quantity to render the gas unmarketable. Natural gas liquids
may be recovered from volume of natural gas, wet after lease separation, at natural gas
processing plants.
Proved Reserves of Natural
Proved reserves of natural gas as of December 31 of the report year are the estimated
Gas
quantities which analysis of geological and engineering data demonstrate with
reasonable certainty to be recoverable in future years from known reservoirs under
existing economic and operating conditions.

Reservoirs are considered proved if economic producibility is supported by actual
production or conclusive formation test (drill stem or wire line), or if economic
producibility is supported by core analyses and/or electric or other log interpretations.

The area of a gas reservoir considered proved includes: (1) that portion delineated by
drilling and defined by gas—oil and/or gas—water contacts, if any; and (2) the
immediately adjoining portions not yet drilled, but which can be reasonably judged as
economically productive on the basis of available geological and engineering data. In the
absence of information on fluid contacts, the lowest known structural occurrence of
hydrocarbons is considered to be the lower proved limit of the reservoir.

Volumes of natural gas placed in underground storage are not to be considered proved
reserves.

For natural gas, wet after lease separation, an appropriate reduction in the reservoir
gas volume has been made to cover the removal of the liquefiable portions of the gas in
lease and/or field separation facilities and the exclusion of non-hydrocarbon gases
where they occur in sufficient quantity to render the gas unmarketable.

For dry natural gas, an appropriate reduction in the gas volume has been made to
cover the removal of the liquefiable portions of the gas in lease and/or field separation
facilities, and in natural gas processing plants, and the exclusion of non-hydrocarbon
gases where they occur in sufficient quantity to render the gas unmarketable.

It is not necessary that production, gathering, or transportation facilities be installed or
operative for a reservoir to be considered proved. It is to be assumed that
compression will be initiated if and when economically justified.
Source: EIA, http://tonto.eia.doe.gov/dnav/ng/TblDefs/ng_enr_sum_tbldef2.asp.

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U.S. Fossil Fuel Resources: Terminology, Reporting, and Summary

Author Contact Information

Gene Whitney
Carol Glover
Section Research Manager
Information Research Specialist
gwhitney@crs.loc.gov, 7-7231
cglover@crs.loc.gov, 7-7353
Carl E. Behrens

Specialist in Energy Policy
cbehrens@crs.loc.gov, 7-8303




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