The Environmental Protection Agency is developing performance standards to limit CO2 emissions from the electric power sector, and refineries may one day face similar regulations. If so, some of the policies for regulating carbon emissions from electric-generating units might be translatable to a greenhouse gas (GHG) performance standard for refineries. However, differences between the electric power and petroleum refining industries may be substantial enough to warrant a re-examination of key regulatory decisions in the power plant rule. This policy brief identifies the key differences and highlights their possible significance for a GHG rulemaking for petroleum refineries under the Clean Air Act. A companion working paper—Regulating Greenhouse Gas Emissions under Section 111(D) of the Clean Air Act: Implications for Petroleum Refineries—discusses the three major steps for rulemaking, policy design questions, potential responses, and their implications as well as examines options for tailoring discussions from power plant regulation, maximizing cost effectiveness, taking into account differences among refineries, and formatting regulation in a way that may best fit them.