The American Petroleum Institute program on atmospheric pollution includes work on the influence of gasoline volatility on automotive evaporation and exhaust emissions. This study concerns automotive performance response to gasoline volatility. Ten cars with and ten cars without exhaust emissions control systems, all 1966 models, were tested. Test fuels bracketed the volatility characteristics of commercially available products. Test temperatures generally covered the range from satisfactory to unsatisfactory performance. Car starting and warm-up performance generally improved with increasing fuel volatility; the degree of improvement varies among cars. No marked effect of exhaust emission control systems was observed. Simulated car aging degraded starting and warm-up performance.