The high global warming potential (GWP) gases include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). These gases have become important to a wide array of industrial technologies and consumer products. HFCs in particular have become important to the safe and costeffective phaseout of chlorofluorocarbons (CFCs), halons and other ozone depleting chemicals worldwide, and can also contribute to efforts to meet emission reduction targets in applications (e.g., foams, refrigeration and air-conditioning) where HFCs have an energy efficiency advantage. The sources of high GWP gas emissions include electric power distribution, refrigeration and air-conditioning, aluminum smelting, HCFC-22 production, aerosols, solvents, foams, fire extinguishing, semiconductor manufacturing, and magnesium production. Weighted by GWP, these gases accounted for about two percent of all U.S. greenhouse gas (GHG) emissions in 1999. However, by 2010, the level of these gases could increase to more than three times 1990 levels. While most of the focus on GHG emission reduction opportunities has been on energy-related CO2 emissions, reduced emissions of the high GWP gases can make a contribution to cost-effective GHG reductions. The purpose of this report is to present EPA's estimates of the potential costs of reducing emissions of the high GWP gases in 2010, and to better characterize the role of the high GWP gases as part of a comprehensive GHG mitigation approach.