Several gasoline supply companies have introduced versions of reformulated gasolines to gain experience in manufacturing, transporting, and marketing this new type of gasoline while providing environmental benefits. This paper describes the evaluation of one such reformulated gasoline on a variety of engine and vehicle technologies.The reformulated gasoline tested in this program is marketed exclusively in the metropolitan St. Louis area. Thus, a side-by-side comparison of fuels representing the average gasoline sold in St. Louis and the reformulated gasoline was made. The reformulated gasoline was blended at the limits of established manufacturing specifications to provide a conservative estimate of the environmental benefits of such a fuel.Emissions and driveability performance of both fuels were tested in cars representing four distinct vehicle technologies. The technology classes represented were non-catalyst, open loop oxidation catalyst, closed loop non-adaptive three-way catalyst, and adaptive learning three-way catalyst equipped vehicles. A total of eight vehicles was tested ranging in model years from 1973 to 1989. The standard Federal Test Procedure with a modified preparation cycle was employed to evaluate the vehicle emission response. Exhaust and evaporative emission measurements were made with complete hydrocarbon speciation and toxic identification.Results of the comparative testing indicated significant reductions of carbon monoxide, total hydrocarbons, oxides of nitrogen, benzene and 1,3 butadiene in 1980 and newer vehicles. Older vehicles (pre-1980) also showed significant reductions of diurnal evaporative hydrocarbon emissions, carbon monoxide, oxides of nitrogen and benzene but increases in hot soak hydrocarbon emissions. All cars showed increases in formaldehyde emissions with the older cars also showing increases in acetaldehyde.The data were used to model the impact of this new gasoline formulation on the St. Louis metropolitan area. The Environmental Protection Agency's MOBILE4 inventory model was employed to project benefits for the years 1995 and 2005 should all gasoline sold in the St. Louis area be the tested reformulated gasoline.