Vehicle emissions tests were conducted using a 1992 model year Toyota Camry for California under the 1975 Federal Test Procedure. Nine fuels of different composition were prepared. Effects of gasoline composition and sulfur content on tailpipe and engine-out emissions were investigated.Exhaust mass emission test results indicated that gasoline distillation properties and sulfur content have large effect on non-methane organic gas emissions.Furthermore, fuel, engine-out, and tailpipe hydrocarbons were speciated and the relationship between fuel and exhaust specific ozone reactivity analyzed.From these studies, it is concluded that aromatics are the largest contributor to the specific ozone reactivity of exhaust emissions and these aromatics, in emissions, are mainly unburned and partly oxidized aromatics from the fuel. Fuel MTBE correlates with exhaust olefins and oxygenates. These products are a large contributor to the ozone reactivity in engine out, but not in tailpipe because of the higher conversion rate of olefins and oxygenates. Fuel Sulfur had little effect on tailpipe hydrocarbon composition.