The Environmental Protection Agency (EPA) regulates the amount of pollution emitted into the atmosphere by stationary combustion sources. To meet these regulations, stationary sources use various techniques to reduce air pollutant emissions, including installing post-combustion emission control technologies. Some post-combustion technologies reduce the emissions of other pollutants besides the one for which they are designed. These concomitant reductions are called cobenefits. The EPA has proposed regulating mercury emissions from coal-fired electric power plants by relying on the results that these post-combustion emission control technologies achieve through cobenefits. The appropriateness of using cobenefits to set emission limits, the reproducibility and reliability of cobenefits, and the likelihood that new technologies specifically designed to reduce mercury emission will be commercially available in the near future are issues of congressional interest. This report will not be updated.