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Posted April 15, 2026What’s in your gasoline? Understanding U.S. motor gasoline formulations ›
Note: Map includes some partial counties and shows both required and Opt-In RFG areas. In California all counties implement a version of the California Reformulated Gasoline Program, not just those required by the Clean Air Act. Alaska, Hawaii, and U.S. territories are exempt from federal volatility regulations. RVP=Reid Vapor Pressure, RFG=Reformulated Gasoline, SIP=State Implementation Plan, AZ CBG=Arizona Clean Burning Gasoline, CA RFG=California Reformulated Gasoline
Motor gasoline in the United States is a blend of hydrocarbons and chemicals, with specific formulas varying by region and season. To meet federal air quality standards, the U.S. Environmental Protection Agency (EPA) and state regulators require different formulations, depending on air quality and location, which affect performance, cost, and emissions. In addition, warmer summer months require a different gasoline formulation than cooler winter months. Key differences between formulations include octane rating, volatility—commonly measured as Reid vapor pressure (RVP)—and emissions. This year, the EPA will relax federal enforcement of summer RVP standards to help reduce gasoline prices.
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