Encyclopedia  |   World Factbook  |   World Flags  |   Reference Tables  |   List of Lists     
   Academic Disciplines  |   Historical Timeline  |   Themed Timelines  |   Biographies  |   How-Tos     
Sponsor by The Tattoo Collection
Main Page | See live article | Alphabetical index


MTBE (methyl tertiary-butyl ether) is a chemical compound that is manufactured by the chemical reaction of methanol and isobutylene. MTBE is produced in very large quantities (more than 200,000 barrels per day in the United States in 1999) and is almost exclusively used as a fuel component in motor gasoline. It is one of a group of chemicals commonly known as oxygenates because they raise the oxygen content of gasoline. At room temperature, MTBE is a volatile, flammable and colorless liquid that dissolves easily in water.

MTBE has been used in U.S. gasoline at low levels since 1979 to replace tetra-ethyl lead as an octane enhancer and to help prevent the engine from "knocking." Since 1992, MTBE has been used at higher concentrations in some gasoline to fulfill the oxygenate requirements set by Congress in Clean Air Act amendments.


Opponents of MTBE note that as an ether, MTBE has a chemical attraction to the water molecule and increases the solubility of other, harmful components of gasoline. Because of this, MTBE often ends up in drinking water, especially in cases where oil storage lanks leak near populated areas, and may make contamination by other compounds more likely. MTBE biodegrades very slowly, remaining in water for decades or more. The oil industry did not test MTBE for its effects on human health before approving it as an additive, as the EPA did not require such tests.

Advocates of MTBE use, such as the oil industry, contend that there are no harmful effects of MTBE in humans. They note that there are no reported cases of a person becoming sick from MTBE in drinking water. Although MTBE has been labelled a "potential human carcinogen" by the Environmental Protection Agency, no carcinogenic properties have been confirmed. Advocates also say that gasoline manufacturers have been forced to add MTBE to gasoline by law.

Opponents respond that any oxygenate would have fulfilled the law, and other, safer compounds (such as ethanol) are available. They claim that MTBE was used instead because it is made by adding methanol to isobutylene, a toxic chemical that the industry would otherwise have to find another way to dispose of.

The clean-up of all MTBE in the U.S. is estimated to cost as much as $140 billion, including breaking down the compound in municipal water supplies and repairing leaky underground oil tanks. Much of the controversy centers around who will have to pay the costs of this clean-up, if such a task is required.

Recent developments

Recent state laws have been passed to ban MTBE in certain areas. A table of state by state information is available here at the Department of Energy website. As of 2004, more than half of all states still permit its use.

In 2000, the EPA drafted plans to phase out the use of MTBE nationwide over four years. Upon taking office, the Bush administration cancelled those plans.

In April of 2002, a California jury found several oil companies guilty of irresponsibly manufacturing and distributing MTBE, stating that the companies acted with malice in failing to warn customers about the dangers of MTBE contamination. There are hundreds of other lawsuits currently active regarding the compound.

Between 2000 and 2004, the top three MTBE manufacturers have donated over $1 million to the United States Republican Party and key members. An amendment to provide blanket immunity from MTBE-related lawsuits was inserted into the House version of the 2003 Energy Bill. The bill failed to pass when six Republicans voted against it, mostly because of that amendment. MTBE lawsuit immunity is likely to remain a political issue in the years to come.

Further reading