A judge of a US superior court has ordered five major oil companies to clean up sites in San Francisco that have been contaminated with the gasoline additive methyl tertiary butyl ether (MTBE). This order was given in response to a lawsuit filed by Communities for a Better Environment (CBE), an environmental organisation. CBE said the settlement would help protect the state's groundwater by making it mandatory for the oil companies to undertake the cleanup task. The oil companies sued were Shell, Chevron, Texaco, Equilon Enterprises, Unocal, Arco, Tosco, Exxon and Mobil. CBE said the companies violated the state's Unfair Competition Act by using MTBE in such a way that it contaminated groundwater.