Alternative fuels may be an effective means for decreasing America’s dependence on imported oil; creating new jobs; and reducing emissions of greenhouse gases, exhaust toxics, and ozone-forming hydrocarbons. However, data regarding in-use fuel economy and maintenance characteristics of alternative fuel vehicles (AFVs) have been limited in availability. This study was undertaken to compare the operating and maintenance characteristics of bi-fuel vehicles (which use liquefied petroleum gas, or propane, as the primary fuel) to those of nominally identical gasoline vehicles. In Texas, liquefied petroleum gas is one of the most widely used alternative fuels. The largest fleet in Texas, operated by the Texas Department of Transportation (TxDOT), has hundred of bi-fuel (LPG and gasoline) vehicles operating in normal daily service. The project was conducted over a 2-year period, including 18 months (April 1997-September 1998) of data collection on operations, maintenance, and fuel consumption of the vehicles under study. This report summarizes the project and its results.