An oxidation catalyst equipped vehicle and several three-way-catalyst (TWC) equipped vehicles were modified to operate on the Federal Test Procedure using gasoline or alcohol fuels. Unburned (hydro)carbon emissions were generally lowest when methanol fuel was used. Oxides of nitrogen (NOx) were reduced an average of more than 50% by using alcohol fuels in contrast to gasoline. Photochemical reactivity comparisons of unburned fuel emissions were made by calculation and also with a 100 cu. ft. smog chamber. Synthetic reproductions (surrogates) of stoichiometric methanol exhaust were less photochemically reactive than gasoline exhaust surrogates for the 8.5:1 compression ratio engine conditions. This effect was observed even though methanol exhaust surrogates were tested at higher hydrocarbon-to-NOx ratios (20:1 vs. 13.8:1) than were the gasoline exhaust surrogates. The exhaust from the stoichiometric TWC-equipped vehicles was extremely low in calculated and experimental reactivities for both methanol and gasoline fuels. This was due to their very low mass emissions and low exhaust hydrocarbon-to-NOx ratios.