In the climate change policy debate, methane capture projects have garnered attention for their ability to mitigate greenhouse gas emissions. Methane capture projects prevent the release of methane, a potent greenhouse gas (GHG), into the atmosphere. The captured methane is generally flared or used for energy purposes. The U.S. Environmental Protection Agency (EPA) has identified four sources of methane with the greatest potential for capture in the near term: landfills, coal mines, agriculture, and oil and gas systems. The amount of methane captured from each will depend on legislative developments, regulations, economics, technology, and outreach. Methane (CH 4 ) constituted approximately 8% of U.S. GHG emissions in 2008. Anthropogenic (human-related) sources of methane in the United States include enteric fermentation, landfills, natural gas systems, coal mines, and manure management. Efforts to reduce emissions of methane—the second-most important GHG after carbon dioxide (CO 2 )—could play a significant role in climate change mitigation. This report will discuss the policy options for addressing methane capture (and their implications), legislative proposals for methane capture, domestic and international sources of methane, opportunities and challenges for methane capture, and federal programs that support methane capture. If policymakers decide to address methane emissions, multiple strategies are available that would either encourage or require methane capture: market-based legislative approaches, such as a cap-and-trade program or emissions fees; carbon offsets or credits as a complementary design element of a market-based approach; emission performance standards; and/or maintaining existing programs and incentives. Policymakers may consider using different strategies for different methane emission sources. These strategies and related issues are discussed below. One option for policymakers is to include methane emission sources as covered entities in a market-based greenhouse gas (GHG) emission control program. Market-based mechanisms that limit GHG emissions can be divided into two types: those that focus on quantity control (e.g., a cap-and-trade program) and those that focus on price control (e.g., emissions fees, often called a carbon tax). Although each approach has its own set of advantages and disadvantages, both would place a price on methane emissions from covered sources. To the extent that they are able, covered entities (those subject to the cap or fee) would likely pass the emissions price through to consumers. For example, if solid waste landfills were subject to a cap or fee based on methane emissions, the landfill operators would likely raise the price of waste disposal to account for the new cost of emissions. Economic theory suggests that a higher waste disposal price would provide a market incentive for consumers to generate less waste, thus decreasing landfill methane emissions. Cap-and-trade and carbon tax proposals in the 111 th Congress generally did not apply to methane emissions from the primary sources of such emissions. The main rationale for excluding some of these groups involved the administrative costs of covering them under an emissions program. As Table 1 indicates, the number of methane emission sources is relatively large compared to their total contribution to U.S. GHG emissions. This is particularly the case for methane emissions from the agriculture sector. Although an even larger number of sources (e.g., industries, automobiles, buildings) generate CO 2 emissions, the vast majority of CO 2 emissions can be addressed by subjecting a relatively small number of entities to an emissions cap. This opportunity exists for CO 2 emissions, because policymakers could apply the emissions cap upstream of the actual emissions, typically where the emission inputs are produced or enter the U.S. economy. Under this approach, policymakers could address CO 2 emissions from fossil fuel combustion and non-energy uses—in aggregate 82% of U.S. GHG emissions—by covering fewer than 2,500 entities. For most methane sources, particularly in the agriculture sector, an analogous opportunity does not exist. In addition, some of the source categories identified in Table 1 may be more amenable to emissions coverage than others. For example, roughly 25% of the methane emissions from natural gas systems comes from field production, which may be impractical to monitor and measure accurately. The remaining 75% primarily involves accidental releases sometimes referred to as fugitive emissions. Landfill methane may offer fewer challenges in terms of measurement, but the largest landfills are already reducing methane emissions pursuant to landfill gas reduction requirements established by the Clean Air Act (42 U.S.C. 7401 et seq . ). Within the framework of a cap-and-trade or carbon tax system, policymakers could encourage methane mitigation activities by allowing methane capture as an eligible offset project or as an emission (or tax) credit. A carbon offset is a measurable reduction, avoidance, or sequestration of GHG emissions from an emission source not covered by a cap-and-trade system. Most of the cap-and-trade proposals offered in the 111 th Congress allowed offsets (under varying conditions) as a compliance alternative. Offsets would likely make an emissions program more cost-effective by (1) providing an incentive for non-regulated sources to generate emission reductions and (2) expanding emission compliance opportunities for regulated entities. The main concern with offset projects is whether or not they represent real emission reductions. For offsets to be real, a ton of CO 2 -equivalent emissions reduced from an offset project should equate to a ton emitted from a capped source, such as a smokestack or exhaust pipe, and would not have occurred without the regulatory incentive. This objective presents challenges because some offset projects are difficult to measure. However, some methane capture projects, such as those from landfills or coal mines, are generally considered to be of higher quality (more credible) than other offset types. These projects are relatively easy to measure and verify, and in many cases would likely not occur if not for the financing provided by an offset market. Therefore, the challenge of proving "additionality" is easier to overcome. The advantage some methane capture projects have over other GHG mitigation activities may spur policymakers to control these methane releases directly (via some of the options discussed), instead of encouraging abatement through an offset market. Moreover, allowing certain activities as offsets, while imposing emission controls or caps on others, may raise issues of fairness. For example, why should specific GHG emission sources, such as electricity generators, be capped while other sources, such as landfill or animal feedlot methane, have the potential to generate financial gain for owners and/or operators through the offset market? Another option for policymakers is to require emission performance standards for particular methane emission sources. This approach has historically represented the core of U.S. federal air pollution policy. New legislation would not be required to pursue the standards approach. The ability to limit methane emissions already exists under various Clean Air Act authorities that Congress has enacted, a point underlined by the Supreme Court in an April 2007 decision, Massachusetts v. EPA . Although the current EPA Administrator has stated a preference for controlling GHG emissions through new legislation, the agency has begun to take actions that could lead to GHG emission performance standards from particular sources. Pursuant to Clean Air Act authority, EPA would achieve emission reductions by setting emission performance standards on each source of pollution, or requiring that sources use a particular type of technology, such as the "best available control technology." Although emission performance standards have proven to be effective through decades of experience, source-by-source regulation often cannot achieve, by itself, a desired emission reduction target at the least collective cost. Moreover, performance standards can be difficult to adjust as circumstances (e.g., technologies) change. On the other hand, they may be less expensive where measurement, administrative, or transaction costs are high relative to emission control costs. This approach may be a practical option for certain specific sources of methane emissions. As discussed later in this report, the federal government currently supports several programs that stimulate methane capture. In addition to these initiatives, which are generally voluntary in nature, since 1996 the Clean Air Act has imposed air emission standards on large solid waste landfills. However, as discussed below, the vast majority of landfills are not covered under the 1996 standards, and there is room to increase the amount of methane captured from solid waste landfills. Moreover, the primary objective of these standards is to reduce the hazardous air pollutants and non-methane organic compounds contained in landfill gas, not to reduce methane emissions for climate-related reasons. Regardless, as mentioned above, the existing Clean Air Act authorities could be used to address a wider universe of methane sources, for the express purpose of controlling GHG emissions, or, as in the case of landfills, for multiple purposes. Because methane can be used as an energy source, the existing marketplace provides some incentive to capture methane for this purpose. If a GHG emission control program were implemented, such a program would increase this incentive by raising the price of traditional high-carbon energy sources (e.g., coal) relative to captured methane. The strength of the incentive would depend on the stringency of the emission control program. The 111 th Congress introduced numerous bills related to methane emissions. One group of bills specified methane as a GHG, promoted biogas production, supported landfill gas recovery projects, and addressed or promoted methane capture. Another set of bills not related to methane capture prohibited permit issuance under the Clean Air Act for methane emissions from biological processes associated with livestock operations, among other provisions, and expanded methane hydrate research. H.R. 2454 , which passed the House on June 26, 2009, contained numerous energy provisions, including a GHG emission cap-and-trade system. If enacted, the cap-and-trade program would have allowed some methane capture activities to generate offsets. However, some methane sources might have been subject to emission performance standards. One enacted piece of legislation ( P.L.