Ten post-1981 and pre-1990 vehicles were tested to determine if the effect of gasoline reformulation would be different than predicted by the EPA complex model. All vehicles passed the IM-240 screening before fuel testing. A nonoxygenated baseline and four oxygenated test fuels with varying levels of sulfur and RVP were tested for exhaust emissions. The emission response of the fuel changes with these vehicles was similar to that predicted by the complex model. However, the NOx emissions of the vehicles in this study were less sensitive to sulfur level than complex model predicts. Also, the oxygenated reformulated gasolines regardless of sulfur level produced greater reductions in NMHC emissions than predicted by the complex model.