The influence of the aromatic hydrocarbons in gasoline on the fuel distillation parameter, as well as the particle number (PN), black carbon (BC), and other regulated gaseous emissions from a passenger car (PC) and light-duty truck (LDT), was assessed by operating two vehicles fueled with U.S. Environmental Protection Agency Tier 3 certification gasoline and two gasoline test fuels over two standard drive cycles. The two gasoline test fuels represent a range of commercial motor gasoline, with one containing less naphthalenes and lower heavy fraction volatility (T80, T90, and final boiling point) than the other. Observations showed that various gasolines have minor impact on both vehicles on regulated gaseous emissions and fuel consumption. Particulate emissions from both vehicles showed similar trends with fuel type, with lower naphthalene containing gasoline produced lower PN and BC emissions. In addition, the effect of fuel on particle emissions varied with vehicle type, drive cycle, and power to weight ratio. Results also showed that lowering the naphthalenes in gasoline produces smaller sized particles. The real-time particle emission time series from both vehicles suggested that the composition and volatility of the gasoline fuels are sensitive parameters in influencing particulate matter emissions. These results could support one possible explanation of the large variations in emission factors reported in the literature when using different gasolines in the same type of vehicle and driving conditions.