VOLKSWAGEN has conducted a number of investigations on a Multi Fuel Vehicle (MFV), designed for variable fuel operation, to determine the influence of fuel composition and clean fuels on exhaust emissions, mainly on ozone forming potential.Results of the tests indicate a small advantage of Phase II Reformulated Gasoline and a greater one for for methanol fuel M85, compared to today's gasoline. For M85 there is an about 25 % lower ozone forming potential. The most critical components in the exhaust of methanol fueled vehicles (M85) are unburned methanol and formaldehyde, forming more than 60 % of the total ozone forming potential. Therefore improvement of cold start and warmup driving during the first two to three minutes is of great importance, because in this time about 90 % of the mentioned components are formed. Lowering the emissions of this period will decrease the ozone forming potential of methanol fueled vehicles significantly and further increase the advantage of methanol fueled concepts.The speciated HC-emissions (aromatics, olefins, paraffins and oxygenates) using five different fuels are presented and the influence of the fue1 composition on the ozone-forming potential of the exhaust is discussed.