In 1998, Communities for a Better Environment (CBE), a San Francisco environmental group, filed suit against Texaco, Chevron, Shell, Arco, Unocal, Tosco, Equilon Enterprises, Exxon, and Mobil, claiming that the companies knew the gasoline additive Methyl tertiary butyl ether (MTBE) could leak into local groundwater supplies. Recently, a California judge approved a settlement agreement which requires five of the companies to clean up MTBE contaminated sites.

CBE hopes the agreement will lead to stronger laws regulating how companies handle MTBE contaminated sites. Currently, MTBE is not a listed substance under California's Safe Drinking Water & Toxic Enforcement Act.

MTBE is a gasoline additive designed to reduce air pollution. Petroleum companies have until the end of 2002 to stop using the additive in California gasoline.