This paper describes the results of a liquefied petroleum gas (LPG) fleet test conducted using para-transit, medium-duty vehicles. The vehicles were part of an active municipal fleet providing daily service on varying operating routes. Over a period of nine months, each vehicle was fueled with a series of butane/propane mixtures. The mixtures tested were HD5 LPG as the baseline fuel, 20 percent butane/80 percent propane, 30 percent butane/70 percent propane, and a final blend of 50 percent butane/50 percent propane by volume. The test vehicles showed improved fuel economy as the butane content increased in the fuel mixture, even without modification to existing LPG fuel systems. The improved fuel performance was consistent with the higher energy content of butane, compared to an equal volume of propane. The vehicles displayed no symptoms of performance or maintenance problems that would be related to operation of the fuel mixtures. Use of the high butane-content mixtures was transparent as compared to operations with standard LPG. Emission tests on three of the six test fleet vehicles were also conducted. The emission results indicate that the 20/80 and 50/50 compositions yielded emission levels that were comparable to emissions from HD5 LPG, within the statistical uncertainty of the data. These tests were conducted in continuation of ARCO's developing database on the emissions, performance, and economics of vehicles operating on mixtures of butane and propane.