MTBE (methyl tertiary-butyl ether) (click here) is a flammable, colorless liquid that dissolves easily in water. It is part of a group of chemicals known as fuel oxygenates. Oxygenates do not occur naturally in gasoline; they are added to increase gasoline’s oxygen content. MTBE and other oxygenates make gasoline burn better, which lowers harmful carbon monoxide and other emissions from vehicles, reducing air pollution.
MTBE was first used in gasoline at low levels in the United States in 1979 to replace lead as an octane enhancer. Starting in 1992, MTBE was used at higher concentrations in some gas to fulfill the oxygenate requirements set by Congress in the 1990 Clean Air Act Amendments (CAA). The CAA required the use of oxygenated gasoline in areas with unhealthy levels of air pollution.
Starting in 1995, the CAA required use of reformulated gasoline (RFG) year-round in cities with the worst ground-level ozone (smog). RFG is gasoline that is specially blended to have fewer polluting compounds than conventional gasoline. As part of the CAA, RFG had to have an oxygen content of at least 2% by weight.
The CAA did not specifically require MTBE to be used as the oxygenate in gasoline. Gas refiners could choose to use other oxygenates, such as ethanol. But MTBE was the main oxygenate in RFG in some areas outside the Midwest, mainly for economic reasons and for its blending characteristics. Unlike ethanol, MTBE could be shipped through existing pipelines, and its volatility is lower, making it easier to meet the emission standards....
