While most studies addressing the fuel effects are based on the Federal Test Procedure (FTP), there are limited studies investigating the fuel effects outside FTP test conditions. In this study, we investigated the differences in exhaust emissions from California Phase 1 to Phase 2 reformulated gasoline over a wide range of speed and ambient temperatures. Eleven catalyst equipped passenger vehicles were tested. The vehicles were comprised of three fuel delivery system configurations, namely, three from carburetor (CARBU), three from throttle body injection (TBI), and five from multi-port fuel injection (MPFI) group. Each vehicle was given 60 tests with the combination of two reformulated fuels: Phase 1 (without oxygenates) and Phase 2 (with oxygenates), three temperatures (50, 75, and 100 °F), and ten speed cycles (average speed ranges from 4 mph to 65 mph). In other words, each vehicle has 30 pairs of Phase 1 and Phase 2 tests under the identical speed and temperature conditions and a total of 330 pairs of test data were analyzed.Paired t-tests were used to analyze the exhaust emissions data from Phase 1 and Phase 2 fuel. The overall exhaust emissions reduction (based on all vehicles) from Phase 1 to Phase 2 fuel for HC, CO, NOx were 17%, 13%, and 11%, respectively. However, only HC and NOx exhaust emissions reduction were found to be statistically significant (α = 0.05). In general, the exhaust emissions reduction derived from this case study is in good agreement with the emissions reduction predicted by the emission factor model (EMFAC) of the California Air Resources Board (CARB).