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  Reformulated gasoline (RFG) is gasoline blended to burn more clearly than conventional gasoline and to reduce smog-forming and toxic pollutants in the air we breathe. The RFG program was mandated by Congress in the 1990 Clean Air Act amendments. The first phase of the RFG program began in 1995 and the second (current) phase began in 2000.

RFG is required in cities with high smog levels and is optional elsewhere. RFG is currently used in 17 states and the District of Columbia. About 30 percent of gasoline sold in the U.S. is reformulated.

http://www.epa.gov/otaq/fuels/gasolinefuels/rfg/index.htm

The air quality benefits RFG has achieved represent a significant part of the country's smog reduction strategy. The RFG program, combined with other industrial and transportation controls aimed at smog reduction, is contributing to the long-term downward trend in U.S. smog levels. About 75 million people breathe cleaner air because of RFG.