Vehicle exhaust emissions tests, using the Federal Test Procedure, were conducted to determine the effect of gasoline sulfur content on the performance of three-way catalysts. The test fuels had sulfur concentrations of 0.01, 0.03, and 0.09 percent.An increase in the fuel sulfur content from 0.01 to 0.09 percent reduced the conversion of hydrocarbons, carbon monoxide, and oxides of nitrogen, resulting in higher tailpipe emissions. The effects were generally small, but statistically significant. The lower conversion was due to poisoning of the catalyst by sulfur species in the exhaust. The poisoning was reversible.