This study evaluates the conversion of one local government's fleet from gasoline to bi-fuel E-85, compressed natural gas, and liquid propane gas powered vehicles at the midpoint of a 10-year conversion plan. This study employs a behavioral model based on the theory of reasoned action to explore factors that influence an individual's perceived and actual use of alternative fuels. Analysis is based on survey data collected from primary drivers of bi-fuel fleet vehicles at the Forest Preserve District of DuPage County, Illinois. Findings show that environmental attitudes do not have a significant effect on actual or perceived use; however, external variables such as fueling convenience, vehicle performance, and the extent of informal communication significantly affect the driver's likelihood of using alternative fuel. The results have implications for fleet managers that could promote regulatory and infrastructural developments to achieve higher rates of alternative fuel use. (Contains 1 figure, 3 tables and 5 notes.)