This evaluation compared six hybrids and six standard diesels in UPS facilities in Phoenix, Arizona. Dispatch and maintenance practices are the same at both facilities. GPS logging, fueling, and maintenance records are used to evaluate the performance of these step delivery vans. The hybrids' average monthly mileage rate was 18% less than the diesel vans. The hybrids consistently were driven afewer number of miles throughout the evaluation period. The hybrids idled more and operating at slower speeds than the diesels, and the diesels spent slightly more time operating at greater speeds, accounting for much of the hybrids' fewer monthly miles. The average fuel economy for the hybrid vans is 13.0 mpg, 23% greater than the diesel vans' 10.6 mpg. Total hybrid maintenance cost/mile of $0.141 was 9% more than the $0.130 for the diesel vans. Propulsion-related maintenance cost/mile of $0.037 for the hybrid vans was 25% more than the $0.029 for the diesel vans. Neither difference was found to be statistically significant. The hybrid group had a cumulative average of 96.3% uptime, less than the diesel group's 99.0% uptime. The hybrids experienced troubleshooting and recalibrationissues related to prototype components that were primarily responsible for the lower uptime figures.