Groundwater contamination prompted states to pass legislation banning or limiting MTBE.

MTBE, the fuel oxygenate of choice up to this point, was found to pose a threat to water quality, prompting many states to issue MTBE bans. Since blenders were still required to oxygenate gasoline because of the Clean Air Act Amendments passed in 1990, they replaced MTBE with environmentally friendly ethanol, increasing demand dramatically.