Outer Limits of the U.S. Extended Continental Shelf: Background and Issues for Congress

February 7, 2024 R47912

Outer Limits of the U.S. Extended Continental
February 7, 2024
Shelf: Background and Issues for Congress
Caitlin Keating-Bitonti
Areas of the ocean within U.S. jurisdiction encompass diverse marine ecosystems and
Analyst in Natural
contain natural resources of economic value and national security interest. The 1982
Resources Policy
United Nations Convention on the Law of the Sea (UNCLOS), to which the United

States is not a party, describes internationally recognized maritime zones. UNCLOS
provides a coastal country with sovereign rights for the purpose of managing,

conserving, exploring, and exploiting natural resources of the seabed and waters within 200 nautical miles (nmi)
of its coastline. The United States generally aligns with the UNCLOS framework for establishing maritime
boundaries. Some coastal countries may pursue research efforts to document and claim areas of the seabed
beyond this 200-nmi limit, known as the extended continental shelf (ECS). An ECS would allow coastal countries
to capitalize on potential resources of this part of the seabed (e.g., critical minerals, oil and gas) as entitled under
UNCLOS.
Under Article 76 of UNCLOS, coastal countries can file a submission concerning the extent of their ECS to the
Commission on the Limits of the Continental Shelf (CLCS), an independent entity created under UNCLOS. The
CLCS considers a coastal country’s submission of geological and geophysical data collected and analyzed to
delineate the outer limits of the ECS. The CLCS does not approve or grant an ECS to a coastal country but makes
recommendations on the outer limits of an ECS based on these data. The CLCS has no mandate to establish
boundaries or resolve boundary conflicts between two coastal countries. Disputes over maritime boundaries must
be resolved between the countries involved in the disagreement.
The U.S. Extended Continental Shelf Project is a federal initiative with an aim to establish the full extent of the
U.S. ECS. The Department of State, the National Oceanic and Atmospheric Administration (NOAA), and the U.S.
Geological Survey (USGS) work together through the U.S. Extended Continental Shelf Project to collect
geological and geophysical data in accordance with UNCLOS Article 76. The U.S. Extended Continental Shelf
Project has analyzed data in each ocean region with potential U.S. ECS.
On December 19, 2023, the Department of State announced the outer limits of the U.S. ECS in seven ocean
regions: the Arctic, Atlantic, Bering Sea, Eastern and Western Gulf of Mexico, Northern Mariana Islands, and
Pacific. The declared U.S. ECS would be approximately 288,000 square nmi (987,700 square kilometers).
According to the Department of State, the United States is ready to file its submission package with the CLCS
upon U.S. accession to UNCLOS. The Department of State also said the United States is open to filing its
submission to the CLCS as a non-party to UNCLOS.
The Senate Committee on Foreign Relations held hearings on UNCLOS during the 112th Congress. Given the
Department of State’s recent announcement about the establishment of the outer limits of the U.S. ECS, Congress
may consider the advantages and disadvantages of U.S. accession to UNCLOS. Congress may choose to
deliberate the extent to which U.S. accession might strengthen the U.S. ability to exercise sovereign rights over
the natural resources in these areas and compare that advantage against potential disadvantages of U.S. accession
to UNCLOS, such as limited economic benefits to U.S. companies and the United States from exploitation of
seabed minerals under the authority of the International Seabed Authority. For example, USGS scientists report
that high concentrations of critical minerals in certain seafloor deposits may serve national security interests.
Several countries party to UNCLOS have shown interest in exploring areas of the Pacific and the Arctic for
potential mineral resources through exploration mining contracts or by filing ECS submissions with U.N. entities
established under UNCLOS. It remains unclear how the international community would respond to a U.S.
submission to the CLCS as a non-party to UNCLOS.
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he U.S. exclusive economic zone (EEZ)1—ocean waters generally between 3 and 200
nautical miles (nmi) seaward from the U.S. coastline—is, according to the National
T Oceanic and Atmospheric Administration (NOAA), the largest in the world.2 The U.S.
EEZ and the seabed beneath it encompass diverse marine ecosystems and contain natural
resources of economic value and national security interest. Areas of the seabed beyond the 200-
nmi outer limit may contain additional natural resources of interest. Several federal departments
and agencies map and characterize areas of the ocean both within the U.S. EEZ and beyond the
200-nmi limit to better understand potential U.S. sovereign rights to the resources in these areas,
among other purposes.3
The United States is not a signatory to the 1982 United Nations (U.N.) Convention on the Law of
the Sea (UNCLOS), which describes internationally recognized maritime zones (Figure 1).
However, some members of the executive branch have stated that some (but not all) portions of
UNCLOS reflect customary international law. For example, the Department of State reports, “The
Convention generally reflects customary international law binding on all countries, including the
provisions in Article 76 pertaining to delineating the outer limits of the continental shelf.”4 In
general, the United States follows the UNCLOS framework for establishing maritime zones. For
example, presidential proclamations have established the U.S. EEZ;5 the U.S. territorial sea, the
area that extends 12 nmi seaward from the U.S. coastline;6 and the U.S. contiguous zone, an area
adjacent to and beyond the territorial sea that extends seaward up to 24 nmi from the U.S.
coastline (Figure 1).7
UNCLOS establishes ocean sovereign rights for coastal countries for the purposes of exploring,
exploiting, conserving, and managing natural resources of the seabed and waters within 200 nmi
of the country’s normal baseline (i.e., low-water line along the coast).8 UNCLOS refers to the
seabed that extends 200 nmi from a coastal country’s baseline and lies beneath the EEZ as the
continental shelf.9 Natural resources that may occur on or in the sediments of the continental shelf
include petroleum resources (e.g., oil, natural gas, methane hydrates), mineral deposits (e.g.,
polymetallic nodules, ferromanganese crusts, polymetallic sulfides),10 and sedentary organisms

1 President of the United States, “Proclamation 5030 of March 10, 1983: Exclusive Economic Zone of the United States
of America,” 48 Federal Register 10605, March 10, 1983.
2 The U.S. exclusive economic zone (EEZ) contains 3.4 million square nautical miles. National Oceanic and
Atmospheric Administration (NOAA), “The United States Is an Ocean Nation,” https://www.gc.noaa.gov/documents/
2011/012711_gcil_maritime_eez_map.pdf.
3 United Nations (U.N.), United Nations Convention on the Law of the Sea of 10 December 1982, Overview and Full
Text, https://www.un.org/depts/los/convention_agreements/convention_overview_convention.htm (hereinafter referred
to as UNCLOS).
4 For example, Department of State, The Outer Limits of the Extended Continental Shelf of the United States of
America: Executive Summary, December 19, 2023, p. 6 (hereinafter referred to as Department of State, U.S. ECS
Executive Summary).
5 UNCLOS, Article 57, describes the EEZ. See footnote 1.
6 UNCLOS, Article 3, describes the territorial sea. President of the United States, “Proclamation 5928 of December 27,
1988: Territorial Sea of the United States of America,” 54 Federal Register 777, January 9, 1989.
7 UNCLOS, Article 33, describes the contiguous zone. President of the United States, “Proclamation 7219 of
September 2, 1999: Contiguous Zone of the United States,” 64 Federal Register 48701, September 8, 1999.
8 UNCLOS, Article 5, describes a normal baseline.
9 UNCLOS, Article 76.
10 For more information about seabed minerals, see CRS Report R47324, Seabed Mining in Areas Beyond National
Jurisdiction: Issues for Congress, by Caitlin Keating-Bitonti.
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(e.g., corals).11 Some of these resources also may occur in areas beyond national jurisdiction—the
seabed and subsoil beyond the 200-nmi continental shelf is referred to as the Area (Figure 1).12
Under Article 76 of UNCLOS, a coastal country interested in expanding its national jurisdiction
beyond the 200-nmi limit of the continental shelf may submit geological and geophysical
evidence for an extended continental shelf (ECS) to a U.N. commission, particularly if the
country sees opportunities to capitalize on potential resources of the seabed in this area (see
“Commission on the Limits of the Continental Shelf,” below).13 An ECS would allow countries to
exercise sovereign rights over the natural resources of the seabed and subsoil beyond the 200-nmi
limit.14
Figure 1. Maritime Zones
(consistent with the United Nations Convention on the Law of the Sea)

Source: Figure modified by the Congressional Research Service. Department of State, “Maritime Zones,”
https://www.state.gov/about-ecs/maritime-zones/.
Notes: Although not a party to the 1982 United Nations Convention on the Law of the Sea (UNCLOS), the
United States generally delineates maritime zones consistent with those established by UNCLOS.
Debate exists regarding whether the United States, as a non-party to UNCLOS, can establish an
ECS. According to the Department of State, the United States does not need to be a party to
UNCLOS to establish the outer limits of its ECS and exercise its sovereign rights and jurisdiction
over this area as provided by UNCLOS Article 76.15 According to the Department of State, the
International Court of Justice concluded that UNCLOS Article 76 is part of customary

11 Sedentary species are immobile organisms that live on the seabed or within the seabed sediments. For more
information about a coastal country’s right to living marine resources under UNCLOS, see CRS Report R47744,
United Nations Convention on the Law of the Sea (UNCLOS): Living Resources Provisions, by Caitlin Keating-Bitonti.
12 UNCLOS, Article 1.
13 For example, see Island Times, “Palau Names 63 Undersea Mounts, Extending Its Undersea Claim,” June 13, 2023,
https://islandtimes.org/palau-names-63-undersea-mounts-extending-its-undersea-claim/.
14 UNCLOS, Article 77. See NOAA, “NOAA’s Participation in the U.S. Extended Continental Shelf Project,”
https://oceanexplorer.noaa.gov/okeanos/explorations/ex1810/ecs/welcome.html.
15 Department of State, “U.S. Extended Continental Shelf Project: Frequently Asked Questions,” https://www.state.gov/
faq-us-ecs-project/.
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international law, meaning both party and non-party coastal countries have rights and obligations
relating to their continental shelves.16 Other stakeholders also contend that the United States
might be able to establish an ECS without acceding to UNCLOS.17 However, several witnesses
who appeared before the Senate Committee on Foreign Relations during prior hearings on
consideration of UNCLOS have stated that U.S. accession to UNCLOS is necessary for the U.S.
ECS to be internationally recognized.18 To date, the Senate has not given advice and consent to
accession to UNCLOS.
For more than a century, Congress has shown interest in ocean mapping activities.19 Congress has
directed and funded certain federal departments and agencies to collect relevant data and
information about the seafloor beneath and adjacent to U.S. ocean waters because “mapping,
exploration, and characterization of the ocean provides basic, essential information to protect and
restore the marine environment, stimulate economic activity, and provide security for the United
States.”20 This report focuses on the mapping activities of the U.S. Extended Continental Shelf
Project, a federal initiative that analyzes data to determine the extent of the U.S. ECS. According
to the Department of State, the project’s work constitutes the largest civilian offshore mapping
effort ever conducted by the United States.21 The U.S. ECS would be approximately 288,000 nmi2
(987,700 square kilometers [km2]),22 or roughly 8% of the total seafloor area beneath the U.S.
EEZ. Based on the size of the U.S. ECS, the U.S. Geological Survey (USGS) estimates the
energy, mineral, and living resources anticipated to be recovered there may be worth billions to
trillions of dollars.23
The U.S. Extended Continental Shelf Project has analyzed data from areas of the Arctic, Atlantic,
Bering Sea, Eastern and Western Gulf of Mexico, Northern Mariana Islands, and Pacific. This
report focuses on U.S. ECS areas in the Arctic Ocean, in the Bering Sea, and in the Pacific Ocean
offshore the Commonwealth of the Northern Mariana Islands, for several reasons.24 First,
projections of shrinking Arctic sea ice cover would presumably increase access to natural
resources located on or in the sediments of the seabed.25 Second, both Arctic and non-Arctic

16 Ibid.
17 For example, Mead Treadwell, “Arctic Horizons: A Primer and Critical Questions on Extending U.S. Territory in the
Arctic Ocean,” Wilson Center, December 19, 2023, https://www.wilsoncenter.org/article/arctic-horizons-primer-and-
critical-questions-extending-us-territory-arctic-ocean (hereinafter, Treadwell, “Arctic Horizons”).
18 For example, see the prepared statements by Don Kraus, Executive Vice President, Citizens for Global Solutions;
John D. Negroponte, Deputy Secretary, Department of State; and Bernard H. Oxman, Professor of Law, University of
Miami School of Law, in U.S. Congress, Senate Committee on Foreign Relations, United Nation’s Convention on the
Law of the Sea (Treaty Doc. 103-39), 110th Cong., 1st sess., September 27 and October 4, 2007, S.Hrg. 110-592
(Washington, DC: GPO 2008); and see the prepared statement of Ambassador John D. Negroponte, Department of
State, in U.S. Congress, Senate Committee on Foreign Relations, The Law of the Sea Convention (Treaty Doc. 103-39),
112th Cong., 2nd sess., May 23, June 14, and June 28, 2012, S.Hrg. 112-654 (Washington, DC: GPO 2013).
19 For an overview of U.S. ocean and coastal mapping activities, see CRS Report R47623, Frequently Asked Questions:
Mapping of U.S. Ocean and Coastal Waters, coordinated by Caitlin Keating-Bitonti.
20 James M. Inhofe National Defense Authorization Act for Fiscal Year 2023 (P.L. 117-263), Division J, Title CIII,
§10301(6).
21 Department of State, “Announcement of U.S. Extended Continental Shelf Outer Limits: Fact Sheet,” December 19,
2023, https://www.state.gov/announcement-of-u-s-extended-continental-shelf-outer-limits-2/.
22 Department of State, U.S. ECS Executive Summary, p. 9.
23 U.S. Geological Survey (USGS), “USGS Law of the Sea,” September 23, 2022, https://www.usgs.gov/centers/
whcmsc/science/usgs-law-sea; and NOAA, “ECS Project,” https://oceanexplorer.noaa.gov/about/what-we-do/media/
ecs-project.pdf
24 Department of State, “U.S. Extended Continental Shelf Project: The U.S. ECS,” https://www.state.gov/the-us-ecs/.
25 For example, see Intergovernmental Panel on Climate Change, “Regional Fact Sheet—Polar Regions,” in the Sixth
(continued...)
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countries show increased interest in exploring and developing potential Arctic resources,
including in establishing ECS areas or investing in Arctic infrastructure.26 Third, certain areas of
the Pacific and Arctic oceans may include natural resources (e.g., critical minerals) that would
serve U.S. national security interests.
Determining the Extent of the Continental Shelf
Determining a coastal country’s ECS requires knowledge of the geophysical characteristics of the
seabed and subsoil.27 The topographic (shape) profile of the seafloor is known as bathymetry.
Formulas set forth in UNCLOS to calculate the extent of the continental shelf beyond the 200-
nmi limit require precise knowledge of the position of the foot of the continental slope—the point
of maximum change in the bathymetric gradient, generally found at the base of the continental
slope.28 The position of the foot of the continental slope is coupled with either (1) the thickness of
sediments on the seafloor or (2) a fixed distance of 60 nmi from the foot of the continental slope
to determine the outer limits of the ECS.29 Different types of data are needed to determine the
position of the foot of the continental slope and these two conditions:
• Seismic data provide information about the thickness of sediments beneath the
seafloor and other characteristics of seafloor sediments.30
• Bathymetric data provide information about the depth of water and profile
information about the seafloor to determine the position of the foot of the
continental slope.31
A coastal country can use one of two formulas described in Article 76 of UNCLOS (or a
combination thereof) to maximize the outer limits of its ECS (Figure 2). The first formula is
based on the thickness of sediment on the seafloor. To determine the outer limits of the ECS
based on this formula, the thickness of the sediment at an outermost fixed point (delineated by a
straight line) is at least 1% of the shortest distance from such point to the foot of the continental
slope.32 For example, if this formula is applied to a point 100 nmi from the foot of the continental

Assessment Report, Working Group I: The Physical Science Basis, 2021, p. 2, https://www.ipcc.ch/report/ar6/wg1/
downloads/factsheets/IPCC_AR6_WGI_Regional_Fact_Sheet_Polar_regions.pdf. For more information about the
changing Arctic, see CRS Report R41153, Changes in the Arctic: Background and Issues for Congress, coordinated by
Ronald O'Rourke.
26 For example, Treadwell, “Arctic Horizons”; RAND Cooperation, “What Does China’s Arctic Presence Mean to the
United States?,” December 29, 2022, https://www.rand.org/pubs/articles/2022/what-does-chinas-arctic-presence-mean-
to-the-us.html; Modern Diplomacy, “U.S. Military May Not Be Ready for Arctic Competition,” December 28, 2023,
https://moderndiplomacy.eu/2023/12/28/u-s-military-may-not-be-ready-for-arctic-competition/; and U.N.,
“Submissions, Through the Secretary-General of the United Nations, to the Commission on the Limits of the
Continental Shelf, Pursuant to Article 76, Paragraph 8, of the United Nations Convention on the Law of the Sea of 10
December 1982,” https://www.un.org/depts/los/clcs_new/commission_submissions.htm.
27 Department of State, “U.S. Extended Continental Shelf Project: About the U.S. ECS Project,” https://www.state.gov/
about-the-us-ecs-project/.
28 UNCLOS, Article 76, paragraph 4(b) and see Ziyin Wu et al., “A New Method to Identify the Foot of the
Continental Slope Based on an Integrated Profile Analysis,” Marine Geophysical Research, vol. 38 (2017), pp. 199-
207.
29 UNCLOS, Article 76, paragraph 4(a).
30 Bureau of Ocean Energy Management (BOEM), “Fact Sheet: Geological and Geophysical (G&G) Surveys,”
https://www.boem.gov/sites/default/files/about-boem/BOEM-Regions/Atlantic-Region/GandG-Overview.pdf.
31 For more information about using bathymetric data to map the seafloor, see CRS Report R47623, Frequently Asked
Questions: Mapping of U.S. Ocean and Coastal Waters, coordinated by Caitlin Keating-Bitonti.
32 UNCLOS, Article 76, paragraph 4(a)(i).
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slope, the extent of the ECS could coincide with the point at which the sediment thickness is 1
nmi thick.33 The second formula is based on distance. It states that the lines delineating the outer
limits of the ECS are not to exceed 60 nmi from the foot of the continental slope.34 In the example
depicted in Figure 2, the formula based on sediment thickness would maximize the ECS
compared with the formula based on the 60 nmi distance. There may be cases where the formula
based on distance would maximize the ECS compared to the formula using sediment thickness.
Figure 2. Formulas to Determine the Extended Continental Shelf
(according to Article 76 of the United Nations Convention on the Law of the Sea)

Source: Figure modified by the Congressional Research Service. Department of State, “U.S. Extended
Continental Shelf Project: About ECS,” https://www.state.gov/about-ecs/.
Notes: The schematic provides a visual for how the extended continental shelf (ECS) is calculated. The foot of
the continental slope is the starting line to determine the ECS. The ECS can be calculated using one of two
formulas. Formula 1 (shown in red) extends the continental shelf up to 60 nautical miles seaward of the foot of
the continental slope. Formula 2 (shown in green) extends the continental shelf up to a seaward distance where
the thickness of the seafloor sediment is at least 1% of the distance to the foot of the continental slope. A coastal
country may use either formula (or a combination thereof) to maximize the outer limits of its ECS.
UNCLOS Article 76 provides two constraints for ECS determinations (Figure 3). The first
constraint is based on distance. It states that the ECS shall not exceed 350 nmi from the
baseline.35 The second constraint is based on water depth. It states that the ECS shall not exceed
100 nmi seaward from the 2,500-meter isobath on the continental shelf.36 If the outer edge of the
continental shelf extends past both constraints, a coastal country can use either line to maximize
its ECS.

33 Sharveen Persand, “A Practical Overview of Article 76 of the United Nations Convention on the Law of the Sea,”
2005, https://www.un.org/depts/los/nippon/unnff_programme_home/fellows_pages/fellows_papers/
persand_0506_mauritius.pdf.
34 UNCLOS, Article 76, paragraph 4(a)(ii).
35 UNCLOS, Article 76, paragraph 5.
36 Ibid. Isobath means a line drawn on a map connecting all points of equal depth below the surface of the water.
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Figure 3. Constraints on the Extent of the Extended Continental Shelf
(according to Article 76 of the United Nations Convention on the Law of the Sea)

Source: Figure modified by the Congressional Research Service. Department of State, “U.S. Extended
Continental Shelf Project: About ECS,” https://www.state.gov/about-ecs/.
Notes: m = meters, in reference to water depth. The schematic provides a visual for the two constraints on the
extended continental shelf (ECS). A coastal country can use either of the constraint lines to maximize its ECS.
Constraint 1 (shown in red) limits the ECS to 350 nautical miles (nmi) from the baseline (i.e., low-water line
along the coast). Constraint 2 (shown in green) states that the ECS shall not exceed 100 nmi from the 2,500-m
water depth line on the continental shelf (i.e., the isobath).
According to UNCLOS Article 78, a coastal country’s rights over its ECS “do not affect the legal
status of the superjacent waters,”37 meaning that claiming an ECS does not afford a country
control over the waters above it.38
Commission on the Limits of the Continental Shelf
Some coastal countries, including the United States, have pursued efforts to map their ECSs.
Under Article 76 of UNCLOS, countries can make a submission to the Commission on the Limits
of the Continental Shelf (CLCS) concerning the extent of their continental shelves.39 The CLCS is
an independent entity created under UNCLOS that consists of 21 members who are experts in
geology, geophysics, or hydrography.40 The CLCS does not approve or grant an ECS to coastal
countries but makes recommendations to countries on the location of their ECS limits. The limits
of the ECS established by a coastal country on the basis of the CLCS recommendations are “final

37 UNCLOS, Article 78.
38 See Department of State, “U.S. Extended Continental Shelf Project: About ECS,” https://www.state.gov/about-ecs/.
39 Annex II of UNCLOS addresses the Commission on the Limits of the Continental Shelf (CLCS).
40 The 21 members of the CLCS serve in a personal capacity. For a list of members and their nationalities, see U.N.,
“Commission on the Limits of the Continental Shelf (CLCS): Members of the Commissions,” https://www.un.org/
depts/los/clcs_new/commission_members.htm.
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and binding.”41 As of February 2024, more than 60 countries have made submissions to the
CLCS.42
Mapping projects are underway by individual countries and through cooperative government
studies to support submissions to the CLCS.43 These submissions involve complex scientific
investigations, and the CLCS bases its recommendations in part on the provided scientific data
and technical analysis. For example, in 2002, the CLCS recommended that Russia provide
additional scientific data and information to accompany its 2001 submission with respect to the
Arctic Ocean.44 In 2015, Russia presented a revised submission to the CLCS.45 In June 2023, the
CLCS “concluded that it was in a position to efficiently conduct the consideration of [Russia’s]
submission.”46
U.S. Extended Continental Shelf Project
Since 2003, the United States has gathered and analyzed geological and geophysical data to
determine the extent of its continental shelf through a federal initiative called the U.S. Extended
Continental Shelf Project. The project’s mission is to “establish the full extent of the U.S.
continental shelf, consistent with international law.”47
The work to determine the outer limits of the U.S. ECS is coordinated by the ECS Task Force, an
interagency body of the U.S. government.48 The ECS Task Force is chaired by the Department of
State, with co-vice chairs from the Department of the Interior (DOI) and NOAA. The Department
of State, NOAA, and USGS conduct the majority of work on the project.49 According to USGS,
these three agencies are “mapping the features of the seafloor and determining sediment thickness
to delineate the outer limits of the U.S. ECS using rules set forth in Article 76 of [UNCLOS].”50
NOAA leads the U.S. effort to collect bathymetric data and has mapped more than 874,700 nmi2

41 UNCLOS, Article 76, paragraph 8.
42 For a list of countries party to UNCLOS that have made submissions to the CLCS, see U.N., “Submissions, Through
the Secretary-General of the United Nations, to the Commission on the Limits of the Continental Shelf, Pursuant to
Article 76, Paragraph 8, of the United Nations Convention on the Law of the Sea of 10 December 1982,”
https://www.un.org/depts/los/clcs_new/commission_submissions.htm.
43 Ibid.
44 U.N., CLCS, “Submissions to the Commission: Submission by the Russian Federation,” https://www.un.org/depts/
los/clcs_new/submissions_files/submission_rus.htm.
45 U.N., CLCS, “Partial Revised Submission of the Russian Federation to the Commission on the Limits of the
Continental Shelf in Respect of the Continental Shelf of the Russian Federation in the Arctic Ocean,” 2015,
http://www.un.org/Depts/los/clcs_new/submissions_files/rus01_rev15/2015_08_03_Exec_Summary_English.pdf.
46 U.N., CLCS, “Progress of Work in the Commission on the Limits of the Continental Shelf,” Statement by the Chair,
CLCS/58/2, September 8, 2023.
47 Department of State, “U.S. Extended Continental Shelf Project: About the U.S. ECS Project,” https://www.state.gov/
about-the-us-ecs-project/.
48 Eleven other government agencies or offices, in addition to the Department of State, NOAA, and the USGS, are part
of the Extended Continental Shelf Task Force. Department of State, “U.S. Extended Continental Shelf Project: About
the U.S. ECS Project,” https://www.state.gov/about-the-us-ecs-project/.
49 The U.S. Extended Continental Shelf Project also relies on preexisting bathymetric data in the public domain and
seismic data obtained from academic institutions and BOEM (Department of State, U.S. ECS Executive Summary, p.
12). U.S. government mapping outside the U.S. EEZ is primarily undertaken by U.S. Navy assets (email
correspondence with NOAA, Congressional Affairs Specialist, Office of Legislative and Intergovernmental Affairs
(OLIA), December 19, 2023).
50 USGS, “Delineating the U.S. Extended Continental Shelf,” September 23, 2022, https://www.usgs.gov/programs/
cmhrp/science/delineating-us-extended-continental-shelf.
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(3 million km2) of the seafloor in support of the U.S. Extended Continental Shelf Project.51 USGS
leads the collection of seismic data for the project.52 NOAA’s National Centers for Environmental
Information (NCEI) stores and makes publicly available all data relevant to the U.S. Extended
Continental Shelf Project, including bathymetric, seismic, and geologic sample data.53 Other
coastal countries also may access data relevant to the delineation of their ECSs through NCEI’s
public repository for global bathymetric and seismic data.54
On December 19, 2023, the Department of State announced the outer limits of the U.S. ECS as
determined by the U.S. Extended Continental Shelf Project.55 This announcement accompanied
the geographic coordinates defining the outer limits of the U.S. ECS in areas of the Arctic,
Atlantic, Bering Sea, Eastern and Western Gulf of Mexico, Northern Mariana Islands, and Pacific
(Figure 4).56 Both current and former members of the CLCS provided assistance to the United
States relating to the analysis and documentation of the U.S. ECS.57 According to the Department
of State, the United States plans to submit this package to the CLCS upon U.S. accession to
UNCLOS but also may consider filing its submission with the CLCS as a non-party to
UNCLOS.58 If the United States were to file its submission with the CLCS, a review of the U.S.
ECS would take place at some future date given the length of the submission queue, which the
CLCS reviews in order of receipt.59
The following sections of the report examine data collected in support of the U.S. Extended
Continental Shelf Project in areas offshore U.S.-affiliated Pacific islands (Guam and the
Commonwealth of the Northern Mariana Islands), as well as in areas offshore Alaska in the Arctic
and Bering Sea.

51 Department of State, U.S. ECS Executive Summary, p. 11.
52 Ibid.
53 See NOAA, National Centers for Environmental Information (NCEI), “U.S. Extended Continental Shelf Data,”
December 6, 2023, https://www.ncei.noaa.gov/products/us-extended-continental-shelf-data (hereinafter referred to as
NOAA, NCEI, “U.S. Continental Shelf Data”).
54 See NOAA, NCEI, “Bathymetric Data Viewer,” https://www.ncei.noaa.gov/maps/bathymetry/.
55 Department of State, “Announcement of U.S. Extended Continental Shelf Outer Limits: Fact Sheet,” December 19,
2023, https://www.state.gov/announcement-of-u-s-extended-continental-shelf-outer-limits-2/.
56 See Department of State, U.S. ECS Executive Summary, pp. 1-100.
57 Current and former members from the CLCS who provided assistance to the United States are from Australia,
Canada, Chile, Denmark, Germany, Japan, Malaysia, Mexico, Mozambique, Netherlands, Norway, Portugal, Trinidad
and Tobago, and the United Kingdom. Department of State, U.S. ECS Executive Summary, p. 13.
58 Department of State, U.S. ECS Executive Summary, p. 6.
59 See footnote Error! Bookmark not defined. and footnote 42.
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Figure 4. Seven Regions of the U.S. Extended Continental Shelf
(as determined by the U.S. Extended Continental Shelf Project)

Source: Map modified by the Congressional Research Service. Department of State, “The U.S. ECS,” December
19, 2023, https://www.state.gov/the-us-ecs/.
Notes: Areas of the U.S. extended continental shelf (ECS) identified by the U.S. Extended Continental Shelf
Project, a federal initiative that aims to establish the ful extent of the U.S. ECS according to international law
(i.e., in alignment with Article 76 of the United Nations Convention on the Law of the Sea). Red lines represent
the outer limits of the U.S. ECS, and red shaded areas delineate the U.S. ECS beyond the 200 nautical mile (nmi)
limit of the continental shelf (thin dark lines), representing 288,000 square nmi (987,700 square kilometers).
Portions of the U.S. ECS are bounded by previously established maritime boundaries with neighboring countries
(i.e., Cuba, Mexico, and Russia). Other portions may overlap with ECS areas of other neighboring countries (i.e.,
the Bahamas, Canada, and Japan).
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U.S. Extended Continental Shelf Project Activities Offshore U.S.-
Affiliated Pacific Islands
The U.S. Extended Continental Shelf Project identified 379 nmi2 (1,300 km2) of the U.S. ECS
located northeast of the Northern Mariana Islands that it claims to be a prolongation of the U.S.
land masses of the island system (Figure 4).60 This area was delineated using the 60 nmi distance
formula and the distance constraint (see “Determining the Extent of the Continental Shelf,”
above).61 In addition, a portion of the U.S. ECS is bounded by Japan to the north.62 According to
the Department of State, “the United States and Japan have not concluded a boundary treaty
delimiting the continental shelf in this region.”63
U.S. Extended Continental Shelf Project Activities in the Arctic
A strategic objective of the 2022 National Strategy for the Arctic Region is for the United States
to “delineate the outer limits of the U.S. continental shelf in accordance with international law.”64
The U.S. Extended Continental Shelf Project identified 151,700 nmi2 (520,400 km2) of the U.S.
ECS in the Arctic that it claims to be a prolongation of the land mass of Alaska (Figure 4).65 The
U.S. ECS in the Arctic represents 53% of the total U.S. ECS. The U.S. Extended Continental
Shelf Project used a combination of the sediment thickness and 60 nmi formulas and both the
distance and depth constraints to delineate the outer limits of the U.S. ECS in this region (see
“Determining the Extent of the Continental Shelf,” above).66 In addition, portions of the U.S. ECS
are bounded by Canada to the east and Russia to the west.67 The United States and Canada do not
have a maritime boundary agreement in the Arctic. However, according to the Department of
State, “Canada has advised the United States that it would not object to the consideration of a
U.S. submission by the [CLCS], without prejudice both to the delineation of the outer limits of its
own continental shelf and to the matters relating to the delimitation of boundaries in this region
between the United States and Canada.”68 In 1990, Russia (then the Soviet Union) and the United
States agreed to a maritime boundary to address overlapping ECS areas in the Arctic.69 To date,
Russia has not asserted ECS claims in any areas that might be considered part of the U.S. ECS.70

60 Department of State, U.S. ECS Executive Summary, pp. 9 and 43.
61 Ibid., p. 11.
62 Ibid., p. 43.
63 Ibid., p. 46.
64 See Strategic Objective 4.2 in White House, National Strategy for the Arctic Region, October 2022, p. 14.
65 Department of State, U.S. ECS Executive Summary, pp. 9 and 15.
66 Ibid., p. 11.
67 Ibid., p. 15.
68 Ibid., p. 19; and Canadian Broadcasting Corporation, “Canada Pledges to Work with U.S. Over Competing Claims to
Arctic Sea Floor,” January 3, 2024, https://www.cbc.ca/news/canada/north/canada-work-with-us-artic-sea-floor-claims-
1.7073547.
69 The Senate gave advice and consent to ratify the maritime boundary agreement in 1991. U.S. Congress, Senate, The
Agreement Between the United States of America and the Union of Soviet Socialist Republics on the Maritime
Boundary, with Annex, Signed at Washington, June 1, 1990, 101st Cong., 2nd sess., September 26, 1990, Treaty Doc.
101-22.
70 The Russian Duma has not approved the maritime boundary agreement. Both countries appear to continue to
provisionally apply the boundary agreement. See Lawfare, “An Off-the-Shelf Guide to Extended Continental Shelves
and the Arctic,” April 21, 2021, https://www.lawfaremedia.org/article/shelf-guide-extended-continental-shelves-and-
arctic.
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The U.S. Extended Continental Shelf Project also identified 51,400 nmi2 (176,300 km2) of the
U.S. ECS located in the Bering Sea that it claims to be a prolongation of the land mass of Alaska
and the Aleutian Islands (Figure 4).71 The U.S. Extended Continental Shelf Project used a
combination of the sediment thickness and 60 nmi formulas and the distance constraint to
delineate the outer limits of the U.S. ECS in this region.72 In addition, the northwest portion of the
U.S. ECS in this area is bounded by the 1990 U.S.-Russia maritime boundary.73 The U.S.
Extended Continental Shelf Project further reports that the U.S. ECS, based on the sediment
thickness and 60 nmi distance formulas, extends beyond the previously agreed-upon maritime
boundary between the United States and Russia.74
Issues for Congress
Knowledge of the limits of a coastal country’s continental shelf allows the country to declare to
other countries the exact extent of its ECS and the sovereign rights it is entitled to exercise within
that area.75 Some stakeholders contend that the U.S. ability to exercise sovereign rights over its
ECS is key to ensuring U.S. economic prosperity and national security.76
Efforts by the United States to map its potential ECS may serve at least two purposes. First, ECS
data may help identify likely “resource-rich realms,”77 thereby providing federal agencies with
the opportunity to manage, conserve, explore, and exploit the resources of the seabed and subsoil
contained within these areas.78 Second, ECS data may elucidate maritime boundaries between the
United States and a neighboring country. Established maritime boundaries with neighboring
countries may be necessary to exercise sovereign rights over the U.S. ECS.
In the 112th Congress, the Senate Committee on Foreign Relations (Committee) held three
hearings on UNCLOS and took no further action.79 UNCLOS has since remained with the
Committee. The U.S. Extended Continental Shelf Project’s work to document the seven regions
with U.S. ECS provides new information for the Committee and other Members of Congress to
consider in their deliberation of UNCLOS.
U.S. Accession to UNCLOS
One common argument for U.S. accession to UNCLOS is that, as a party to the convention, the
United States could access the CLCS’s procedures for according international recognition and

71 Department of State, U.S. ECS Executive Summary, pp. 9 and 27.
72 Ibid., p. 11.
73 Ibid., p. 27.
74 Ibid.
75 UNCLOS, Article 77.
76 For example, see James Kraska, “Strategic Implication of the U.S. Extended Continental Shelf,” Wilson Center,
December 19, 2023, https://www.wilsoncenter.org/article/strategic-implication-us-extended-continental-shelf
(hereinafter referred to as Kraska, “Strategic Implication of U.S. ECS”).
77 NOAA, “NOAA’s Participation in the U.S. Extended Continental Shelf Project,” https://oceanexplorer.noaa.gov/
okeanos/explorations/ex1810/ecs/welcome.html.
78 USGS, “Delineating the U.S. Extended Continental Shelf,” September 23, 2022, https://www.usgs.gov/programs/
cmhrp/science/delineating-us-extended-continental-shelf.
79 U.S. Congress, Senate Committee on Foreign Relations, The Law of the Sea Convention (Treaty Doc. 103-39), 112th
Cong., 2nd sess., May 23, June 14, and June 28, 2012, S.Hrg. 112-654 (Washington, DC: GPO 2013), pp. 1-318.
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legal weight to the U.S. ECS.80 A recommendation from the CLCS on the U.S. ECS would be
final and binding.81 In the 118th Congress, S.Res. 466 identifies that “lack of full-party
membership to UNCLOS limits the access and influence of the United States to critical territorial
dispute management, including matters involving pursuit and competition of extended outer
continental shelf submissions” and relying on customary international norms is “not sufficient.”
According to the Department of State, the United States is “open to filing its submission with the
Commission as a non-party” to UNCLOS.82 It remains unclear if the CLCS would consider a U.S.
submission in these circumstances.83 Further, it remains unclear how the international community
would respond to such a U.S. submission. One source reports objections from Russia, with a
member of the Russian Federation Council quoted as saying, “the Americans act without any
international legal basis at all, which means the international community has every right not to
recognize new borders.”84 A second source quoted the Chair of Russia’s Ministry for the
Development of the Russian Far East and Arctic as saying, “the unilateral expansion of boarders
in the Arctic is unacceptable and can only lead to increased tensions,” in reference to the U.S.
ECS announcement.85
In some instances, the United States has exercised sovereign rights over natural resources in areas
of its ECS without being a party to UNCLOS. For example, DOI has offered the westernmost
ECS area of the Gulf of Mexico, commonly known as the Western Gap, for oil and gas
development (see Figure 4).86 Some stakeholders reference DOI’s leases in the Western Gap as
examples to refute the claim that U.S. accession to UNCLOS is necessary for the United States to
exercise sovereign rights over the natural resources of the seabed and subsoil.87 The United States
has exercised sovereign rights over the natural resources in the Western Gap without objection
from the international community; however, the United States has not exercised sovereign rights
over the natural resources located in areas of the U.S. ECS without agreed-upon maritime
boundary with a neighboring country (see “Delimitation of and Disputes over Maritime
Boundaries,” below). Similarly, the United States has not exercised sovereign rights in an area of
the U.S. ECS adjacent to the Area (i.e., areas beyond national jurisdiction).88

80 For example, see the prepared statement by John D. Negroponte, Deputy Secretary, Department of State, in U.S.
Congress, Senate Committee on Foreign Relations, United Nation’s Convention on the Law of the Sea (Treaty Doc.
103-39), 110th Cong., 1st sess., September 27 and October 4, 2007, S.Hrg. 110-592 (Washington, DC: GPO 2008), p.
12.
81 See footnote 41.
82 Department of State, U.S. ECS Executive Summary, pp. 49-52.
83 For example, see Kraska, “Strategic Implication of U.S. ECS.”
84 James Brooke, “Echoing Trump’s Offer to Buy Greenland, America Quietly Doubles Its Claim to Arctic Seabed,”
New York Sun, January 4, 2024, https://www.nysun.com/article/echoing-trumps-offer-to-buy-greenland-america-
quietly-doubles-its-claim-to-arctic-seabed.
85 Mike Eckel et al., “Under Sea, Under Stone: How the U.S. Claimed Vast New Arctic Territory–In an Unusual Way,”
Radio Free Europe/Radio Liberty, https://www.rferl.org/a/arctic-sea-claims-interactive-map/32793427.html.
86 For example, BOEM, “Western Gulf of Mexico Lease Sale 180 Information,” https://www.boem.gov/oil-gas-energy/
leasing/western-gulf-mexico-lease-sale-180-information.
87 For example, see the prepared statement of Steven Groves, Bernard and Barbara Lomas Fellow, Heritage
Foundation, in U.S. Congress, Senate Committee on Foreign Relations, The Law of the Sea Convention (Treaty Doc.
103-39), 112th Cong., 2nd sess., May 23, June 14, and June 28, 2012, S.Hrg. 112-654 (Washington, DC: GPO 2013).
88 The U.S. Extended Continental Shelf Project identified an area of the U.S. ECS offshore California, along the
Mendocino Ridge, that does not overlap with or extend to any neighboring country’s ECS (Department of State, U.S.
ECS Executive Summary, p. 6).
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U.S. Extended Continental Shelf Areas with Potential Resources
The extent of scientific evidence has been a factor underpinning ECS claims. Countries have
contested ECS claims, citing insufficient scientific data as the reason for their objection.89
Congress may consider providing resources to U.S. agencies (e.g., the Department of State,
NOAA, USGS) for additional research and data collection to counter other countries’ objections
on these grounds.90 The U.S. Extended Continental Shelf Project reports that 37 separate cruises
collected bathymetric data for the project, totaling nearly 2.5 years of sea time.91 According to
NOAA, while research cruises were collecting bathymetric data for the U.S. Extended
Continental Shelf Project, the agency spent approximately $52 million (in non-inflation adjusted
funding) on these cruises and their staffing support and to fund the project office.92 Since 2018,
NOAA has spent approximately $800,000 per year on management and analysis of these
bathymetric data.93
The ECS delineated by the U.S. Extended Continental Shelf Project may protect future U.S.
economic opportunities.94 Because an ECS falls under national jurisdiction, activities such as
seabed mining of hardrock minerals on the ECS would be subject to domestic regulations. The
International Seabed Authority (ISA), an autonomous organization established by UNCLOS,
regulates all seabed mining activities taking place under the high seas, including the approval of
exploration and exploitation contracts to public and private mining enterprises, provided they are
sponsored by a country party to UNCLOS.95 An established ECS would prohibit foreign countries
from pursuing exploration or exploitation contracts through the ISA for areas located within
another country’s ECS. In addition, an extension of the outer limits of the U.S. ECS to include
mineral-rich areas would be a potential strategy to access mineral resources under sole U.S.
authority, rather than under the authority of the ISA. Available technology, among other factors,
currently limits the exploitation of seabed resources; however, some countries show increasing
interest in the exploration of seabed minerals.96

89 For example, some countries challenged Russia’s 2001 submission for its ECS in the Arctic due to a lack of
sufficient scientific evidence (see “Reaction of States to the Submission Made by the Russia Federation to the
Commission on the Limits of the Continental Shelf” at U.N., “Submission to the Commission: Submission by the
Russia Federation,” updated on June 30, 2009, https://www.un.org/depts/los/clcs_new/submissions_files/
submission_rus.htm).
90 U.S. Extended Continental Shelf Project data acquisition and analysis efforts are funded through NOAA National
Ocean Service’s Navigation, Observations, and Positioning Activity (email correspondence between CRS and NOAA
OLIA, December 19, 2023).
91 Department of State, U.S. ECS Executive Summary, p. 9.
92 According to the Department of State, cruises collected bathymetric data for the project between 2003 and 2018
(Department of State, “U.S. Extended Continental Shelf Project: Data Collection,” https://www.state.gov/data-
collection-us-ecs-project/). Email correspondence with NOAA, Congressional Affairs Specialist, OLIA, January 25,
2024.
93 Ibid.
94 Bloom, “Five Takeaways.”
95 A primary reason the United States did not sign UNCLOS relates to U.S. objections to the International Seabed
Authority (ISA). Some stakeholders contend U.S. accession to UNCLOS would limit economic benefits to U.S.
companies and the United States from exploitation of seabed minerals under the authority of the ISA. For more
information about the ISA and the U.S. position on seabed mining in areas beyond national jurisdiction, see CRS
Report R47324, Seabed Mining in Areas Beyond National Jurisdiction: Issues for Congress, by Caitlin Keating-
Bitonti.
96 For example, see ISA, “Exploration Contracts,” https://www.isa.org.jm/exploration-contracts/. The Cook Islands and
Japan are both exploring seabed mining opportunities within their exclusive economic zones. James R. Hein et al.,
“Critical Metals in Manganese Nodules From the Cook Islands EEZ, Abundances and Distributions,” Ore Geology
(continued...)
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A secure domestic supply of seabed minerals of national strategic importance (i.e., critical
minerals) located in areas of the U.S. ECS could reduce U.S. dependence on foreign countries, in
particular China, for these resources.97 For example, certain areas of the central and northwest
Pacific Ocean have mineral deposits (polymetallic nodules) or crusts that are rich in cobalt,
manganese, and other critical minerals.98 The U.S. ECS located northeast of the Northern Mariana
Islands represents 0.01% of the total U.S. EEZ.99 Congress may be interested in whether any of
the data collected by the U.S. Extended Continental Shelf Project in areas offshore Hawaii and
U.S. island territories in the Pacific may support additional U.S. ECS areas, particularly areas that
may contain abundant mineral resources (Figure 5).
Figure 5. Selected Cruise Surveys That Collected Extended Continental Shelf Data
Offshore Hawaii and U.S.-Affiliated Pacific Islands

Source: Congressional Research Service (CRS), using cruise survey data provided to CRS by the National
Oceanic and Atmospheric Administration’s (NOAA’s) National Centers for Environmental Information (NCEI)
on August 3, 2023, and U.S. extended continental shelf (ECS) boundaries published by the Department of State
(see “U.S. Extended Continental Shelf,” https://www.state.gov/the-us-ecs/). The exclusive economic zone (EEZ)
boundaries were derived from the Sovereign Limits database (sovereignlimits.com).
Notes: The map shows four of the five cruise surveys that col ected data used for the U.S. Extended
Continental Shelf Project (orange) and seven of the nine cruise surveys that NOAA considers possibly relevant
to the U.S. ECS (green; NOAA, NCEI, “U.S. Extended Continental Shelf Data,” https://www.ncei.noaa.gov/
products/us-extended-continental-shelf-data). Thin blue lines denote the 200-nautical mile EEZ of coastal
countries. CRS was unable to obtain data for three cruises; CRS requested these files from NCEI on December
6, 2023.

Reviews, vol. 68 (2015), pp. 97-116; Ocean Minerals LLC, “The Cook Islands,” https://www.omlus.com/ocean-
minerals-llc-cook-islands/; Odyssey Marine Exploration, “Cook Islands Polymetallic Nodule Exploration Program,”
https://www.odysseymarine.com/cookislands; and Asia Times, “Japan Dives into Rare Earth Mining Under the Sea,”
January 10, 2023, https://asiatimes.com/2023/01/japan-dives-into-rare-earth-mining-under-the-sea/ (hereinafter referred
to as Asia Times, “Japan Mining Under the Sea”).
97 Kraska, “Strategic Implication of U.S. ECS.” China holds 31 exploration contracts from the ISA (ISA, “Exploration
Contracts,” https://www.isa.org.jm/exploration-contracts/).
98 USGS, “Global Marine Mineral Resources,” June 15, 2022, https://www.usgs.gov/centers/pcmsc/science/global-
marine-mineral-resources; and ISA, “Exploration Areas,” https://www.isa.org.jm/exploration-contracts/exploration-
areas/.
99 Department of State, U.S. ECS Executive Summary, p. 9.
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The establishment of the U.S. ECS in the Arctic and the ECS of other Arctic coastal countries
could signal to non-Arctic countries (e.g., China100) that existing and potential Arctic resources
are under the legal jurisdiction of the five Arctic coastal nations.101 In the Arctic Ocean, USGS
scientists have estimated undiscovered conventional oil and gas resources,102 and have identified
high concentrations of critical minerals in seafloor deposits sampled more than 300 nmi north of
Alaska.103 USGS scientists also are studying ECS data to better understand the distribution of gas
hydrates, a potentially valuable energy resource, in the Bering Sea.104 The U.S. ECS in the Arctic
and Bering Sea combined represents 6% of the U.S. EEZ.105 Canada, Denmark (for Greenland),
Norway, and Russia have each made at least one submission to the CLCS.106 The majority of the
Arctic seabed is under the national jurisdictions of the five Arctic coastal countries.107 In August
2023, the CLCS provided Russia with recommendations relating to its 2001 (and 2015 revised)
ECS submission related to the Arctic Ocean.108 These recommendations may help secure Russia’s
legal rights to resources across a portion of the Arctic’s seafloor.109
Resources identified in portions of the U.S. ECS could add to current resources of U.S. supplies
of critical minerals and other commodities. Should the United States wish to exercise sovereign
rights over the natural resources located on the U.S. ECS, Congress may consider several
potential issues. An ECS in the seven regions identified by the U.S. Extended Continental Shelf
Project would increase the area of continental shelf under U.S. jurisdiction by approximately
288,000 nmi2 (987,700 km2), roughly 8% of the total seafloor area beneath the U.S. EEZ.110 This
increase in submerged land may necessitate additional resources for the DOI, which has
jurisdiction over the submerged lands of the U.S. outer continental shelf (OCS) for energy

100 In 2018, China released its national Arctic policy. In the national Arctic policy, China stated, “China is an important
stakeholder in Arctic affairs” and declared China a “near-Arctic State.” The People’s Republic of China, China’s Arctic
Policy, January 2018, https://english.www.gov.cn/archive/white_paper/2018/01/26/content_281476026660336.htm. In
recent years, China’s polar icebreakers have collected geological and geophysical data in the Arctic Ocean, and China
has invested in several infrastructure projects in the region (e.g., RAND Cooperation, “What Does China’s Arctic
Presence Mean to the United States?,” December 29, 2022, https://www.rand.org/pubs/articles/2022/what-does-chinas-
arctic-presence-mean-to-the-us.html; and Modern Diplomacy, “U.S. Military May Not Be Ready for Arctic
Competition,” December 28, 2023, https://moderndiplomacy.eu/2023/12/28/u-s-military-may-not-be-ready-for-arctic-
competition/).
101 For example, Abbie Tingstad, “The U.S. Is Taking an Important, But Imperfect Step in Initiating Extended
Continental Shelf Claims – What Are the Implications for the Arctic?,” Wilson Center, December 19, 2023,
https://www.wilsoncenter.org/article/us-taking-important-imperfect-step-initiating-extended-continental-shelf-claims-
what-are. The five Arctic coastal countries (i.e., countries with mainland coasts that front onto the waters of the Arctic
Circle) are Canada, Denmark (by virtue of Greenland), Norway, Russia, and the United States.
102 Kenneth J. Bird et al., Circum-Arctic Resource Appraisal: Estimates of Undiscovered Oil and Gas North of the
Arctic Circle, USGS Fact Sheet 2008-3039, 2008, p. 4.
103 USGS, “Delineating the U.S. Extended Continental Shelf,” September 23, 2022, https://www.usgs.gov/programs/
cmhrp/science/delineating-us-extended-continental-shelf; and USGA, “Critical Minerals in the EEZ,” June 5, 2020,
https://www.usgs.gov/news/featured-story/critical-minerals-eez.
104 Ibid.
105 Department of State, U.S. ECS Executive Summary, p. 9.
106 For more information about Arctic coastal country submissions to the CLCS, see CRS Report R41153, Changes in
the Arctic: Background and Issues for Congress, coordinated by Ronald O'Rourke; and see footnote 42.
107 Only a small portion of the Arctic seabed would be under the jurisdiction of the ISA. Bloom, “Five Takeaways.”
108 U.N., “Submissions to the Commission: Partial Revised Submission by the Russian Federation,” updated August 17,
2023, https://www.un.org/depts/los/clcs_new/submissions_files/submission_rus_rev2.htm.
109 Some estimate that Russia’s ECS claim in the Arctic encompasses almost 70% of the Arctic Ocean’s seafloor (e.g.,
The Maritime Executive, “Russia Insists on an Expanded Boundary in the Arctic Ocean,” December 10, 2023,
https://maritime-executive.com/article/russia-insists-on-an-expanded-boundary-in-the-arctic-ocean.)
110 Department of State, U.S. ECS Executive Summary, p. 9.
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development,111 and for NOAA’s National Marine Fisheries Service, which has authority over the
management of bottom-dwelling marine organisms living on or in the sediments of the U.S.
OCS.112 In addition, the exploitation of resources from U.S. ECS areas could increase federal
revenues. For example, the exploitation of oil, gas, hydrogen, or seabed minerals on the U.S. ECS
could generate revenues flowing to the federal government from lease sales, royalties on
production, and rental fees.113 Congress may consider this possibility when evaluating federal
revenue and royalty policies, which could also affect federal policies for sharing these potentially
new sources of federal revenues with coastal states.114
Delimitation of and Disputes over Maritime Boundaries
Only a country with rights and standing can challenge an ECS backed by geological and
geophysical data, as required by Article 76 of UNCLOS. Disputes over maritime boundaries must
be resolved between the countries involved in the disagreement. Although the CLCS can work to
delineate ECS areas, it has no mechanism for resolving international disputes.115
The United States has agreed to maritime boundaries that include areas of the U.S. ECS in
bilateral agreements with Cuba, Mexico, and Russia,116 (the 1990 U.S.-Russia maritime boundary
is discussed in “U.S. Extended Continental Shelf Project Activities in the Arctic,” above). In
2000, the United States and Mexico signed a treaty (commonly known as the Western Gap
Treaty) delimiting the areas of their ECS in the Gulf of Mexico.117 Following the Senate’s consent
to ratification of this treaty, the United States has exercised sovereign rights over the natural
resources in its ECS in the Western Gap.118
On December 18, 2023, President Biden transmitted two bilateral maritime treaties—one for
Mexico and one for Cuba—to the Senate for advice and consent.119 Both of these bilateral treaties
delineate maritime boundaries of an area of the ECS in the Eastern Gulf of Mexico, commonly
known as the Eastern Gap.120 The two U.S. ECS areas in the Gulf of Mexico established by the

111 The Outer Continental Shelf Lands Act defines outer continental shelf to mean areas for which “the subsoil and
seabed appertain to the United States and are subject to is jurisdiction and control or within the exclusive economic
zone of the United States” (43 USC §1331(a)(1)).
112 16 U.S.C. §§1801 et seq.
113 BOEM, “Revenue Sharing,” https://www.boem.gov/oil-gas-energy/energy-economics/revenue-sharing.
114 Treadwell, “Arctic Horizons.”
115 Department of State, “U.S. Extended Continental Shelf Project: Frequently Asked Questions,”
https://www.state.gov/faq-us-ecs-project/.
116 For a list of countries with which the United States has entered into maritime boundary agreements, see Department
of State, “U.S. Maritime Boundaries: Agreements and Treaties,” https://www.state.gov/u-s-maritime-boundaries-
agreements-and-treaties/.
117 U.S. Congress, Senate, Treaty Between the Government of the United States of America and the Government of the
United Mexican States on the Delimitation of the Continental Shelf in the Western Gulf of Mexico Beyond 200 Nautical
Miles, Signed at Washington on June 9, 2000, 106th Cong., 2nd sess., July 27, 2000, Treaty Doc. 106-39.
118 Ibid.
119 White House, “Message to the Senate Transmitting Two Maritime Treaties,” December 18, 2023,
https://www.whitehouse.gov/briefing-room/presidential-actions/2023/12/18/message-to-the-senate-transmitting-two-
maritime-treaties/.
120 Treaty Between the Government of the United States of America and the Government of the United Mexican States
on the Delimitation of the Maritime Boundary in the Eastern Gulf of Mexico, signed January 18, 2017,
https://www.state.gov/u-s-maritime-boundaries-agreements-and-treaties/; and Treaty Between the Government of the
United States of America and the Republic of Cuba on the Delimitation of the Continental Shelf in the Eastern Gulf of
Mexico Beyond 200 Nautical Miles, signed January 18, 2017, https://www.state.gov/u-s-maritime-boundaries-
agreements-and-treaties/.
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Outer Limits of the U.S. Extended Continental Shelf

U.S. Extended Continental Shelf Project are bounded by maritime boundaries described in the
bilateral treaties.121
Some areas of the U.S. ECS have unresolved maritime boundaries with neighboring countries. To
resolve them, the United States and a neighboring country must first agree to a maritime
boundary, after which the President would transmit that agreement to the Senate for its advice and
consent. For example, in the Arctic, the U.S. ECS overlaps with ECS areas of Canada.122 Both
countries worked cooperatively to collect data needed to delineate the ECS in a two-ship
operation involving the U.S. Coast Guard Cutter Healy and the Canadian Coast Guard ship Louis
S. Saint Laurent.123 According to the Department of State, this type of scientific and diplomatic
cooperation has “saved millions of dollars for both countries, provided data both countries need,
ensured that data are collected only once in the same area, and increased scientific and diplomatic
cooperation.”124
The United States and Canada also have unresolved ECS boundaries in the Atlantic.125 The
United States and the Bahamas have unresolved ECS boundaries in the Atlantic, as well.126
In the Pacific, the United States has unresolved maritime boundaries with Japan. The U.S. ECS
(by way of the Northern Mariana Islands) overlaps with ECS areas of Japan in its Ogasawara
Plateau Region,127 an area Japan reportedly may be exploring for potential resources.128
According to the Department of State, the United States and Japan have consulted on overlapping
areas of the ECS in this region of the Pacific.129
Implications for UNCLOS
The U.S. Extended Continental Shelf Project provides Congress with a new information to weigh
in its potential deliberation of U.S. accession to UNCLOS. A month prior to the Department of
State’s December 19, 2023, announcement of the U.S. ECS, Senators introduced S.Res. 466,
which “urge[d] the United States Senate to give its advice and consent to the ratification of the
UNCLOS.” Other Members of Congress considering seabed mining options wrote a letter to
Secretary of Defense Lloyd Austin on December 7, 2023, calling on the Department to “explore
every avenue to strengthen our rare earth and critical minerals supply chains.”130 The letter
invokes the participation of the United States as an observer state in the ISA, but does not
explicitly mention the option of U.S. accession to UNCLOS.131

121 Department of State, U.S. ECS Executive Summary, pp. 35-37, 39-41.
122 Ibid., p. 19.
123 Department of State, “U.S. Extended Continental Shelf Project: Data Collection,” https://www.state.gov/data-
collection-us-ecs-project/.
124 Department of State, “U.S. Extended Continental Shelf Project: International Cooperation,” https://www.state.gov/
international-cooperation-us-ecs-project/.
125 Department of State, U.S. ECS Executive Summary, p. 21.
126 Ibid.
127 Ibid., p. 46.
128 Asia Times, “Japan Mining Under the Sea.”
129 Ibid.
130 Letter from 31 Members of Congress to Lloyd Austin, Secretary of Defense, December 7, 2023,
https://wittman.house.gov/uploadedfiles/20231207_-_wittmanstefanik_-
_national_security_impacts_of_seabed_mining_-_signed.pdf.
131 Ibid.
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Author Information

Caitlin Keating-Bitonti

Analyst in Natural Resources Policy

Acknowledgments
Calvin Desouza, Geospatial Information Systems Analyst, and Amber Wilhelm, Visual Information
Specialist, contributed to the maps and figures.

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