Sixty-six diesel-powered taxicabs, paired with an equal number of gasoline powered cabs, are being operated in three taxicab fleets in New York City. Identical cabs are powered either with Chrysler 225 CID gasoline engines or with Nissan 198 CID diesel engines. Data from both sets of cabs are analyzed to determine differences in reliability, maintenance, exhaust emissions and fuel economy. Data currently reported covers a period where individual taxicabs have accumulated between 70,000 and 110,000 miles of service. The diesel fleet shows improvement in fuel economy and exhaust emissions over the gasoline fleet.