The results of an extensive case history evaluation of methane-fueled vehicles are presented. A total of 67 methane-fueled fleet operators throughout the United States were contacted. The questionnaire sent to the operators was designed to procure: (1) general information regarding the fleet (length of time the methane-fueled fleet has been operating and types and number of vehicles converted); (2) information on the fuel and vehicle fuel system (source of methane, heating value of gas, and vehicle fuel tank capacity); (3) vehicle fuel consumption and mileage information; (4) cost information; and (5) information regarding operational difficulties attributable to conversion for operation on methane. A total of 28 responses were obtained, encompassing nearly 3,500 vehicles. Data from the study have been compiled into several comprehensive tables. The ranges of various parameters are discussed, as well as the operation difficulties that were reported.