Winter use of oxygenated fuels was mandated in 39 major non-attainment areas.

The 1990 Clean Air Act Amendment, considered to be landmark legislation because it focused on fuel rather than engines to reduce emissions, required the use of fuel oxygenates, paving the way for a big increase in the demand for ethanol when MTBE, largely the oxygenate of choice in the early 1990s, was discovered to be a groundwater contaminant.