Effects of methyl tertiary-butyl ether (MTBE) and tertiary-amyl methyl ether (TAME) on emissions were compared in a fleet of ten 1989 model year vehicles. Test fuels containing 11.5 vol.% MTBE or 12.7 vol.% TAME were blended in a base fuel representing federal emission certification fuel. The oxygen content of both fuels was about 2.0 wt.%. No significant differences were found between the two fuels in exhaust mass HC, NMHC, CO, or NOx; in exhaust or evaporative toxic air pollutants, benzene, 1,3-butadiene, acetaldehyde, or total toxic emissions; or in evaporative hot soak emissions. The only differences found to be significant at the 95% level were in mass and estimated reactivity-weighted diurnal evaporative emissions, for both of which the TAME fuel was about 24% lower than the MTBE fuel; and in formaldehyde emissions, which were 28% higher with the TAME fuel.