Reformulated gasoline is a cleaner-burning gasoline that reduces smog and other air pollution. Federal law mandates the sale of reformulated gasoline in nine metropolitan areas with the worst ozone smog: Baltimore, Chicago, Hartford, Houston, Los Angeles, Milwaukee, New York, Philadelphia, and San Diego. Some other cities voluntarily require reformulated gasoline. About 20 to 25 percent of the gasoline sold in the United States is reformulated. It has the same effect on the environment as taking seven million cars off the road, according to EPA. Reserves An economically recoverable quantity of crude oil and gas that has not yet been produced from reservoirs.