Recently, the Environmental Protection Agency (EPA) has required adding oxygenates to fuels used in “air quality non-attainment” areas. Mostly, these are large metropolitan areas such as Los Angeles. Oxygenates are exactly what they sound like: additives that blend oxygen into the gasoline. The target is to add 2 percent oxygen to the gasoline, which, according to Wusz, has the effect of leaning the air/fuel ratio of the fuel. This can mean a significantly leaner air/fuel ratio compared to nonoxygenated gasoline. This used to be mandated only in the winter months and served to reduce hydrocarbon emissions. But in Los Angeles, for example, oxygenated fuels are now here to stay. At the start of 1995, approximately 35 percent of all gasoline sold in the U.S. was oxygenated.