Vehicle tests showed that evaporative emissions were increased significantly by adding 10 percent ethanol to gasoline, but were increased less with 15 percent MTBE in gasoline. The quantity of ethanol or MTBE in evaporative emissions was investigated in laboratory tests. Exhaust HC, CO, and NOx emissions from a car without closed-loop fuel control were significantly lower with the ethanol and MTBE fuel blends than with gasoline. For cars equipped with closed-loop carburetors, the absolute differences in exhaust emissions among the fuels were small. Fuel economy and drive-ability were worse with ethanol and MTBE fuel blends than with gasoline.