This paper presents thermodynamic analyses of ten different scenarios for using natural gas to power motor vehicles. Specifically, it presents a comparison between different types of automotive vehicles using fuels made from natural gas feedstock. In comparing the various fuel-vehicle options, a complete well-to-wheel fuel cycle is considered. This approach starts with the well at which the feedstock is first extracted from the ground and ends with the power finally delivered to the wheels of the vehicle. This all-inclusive comparison is essential in order to accurately and fairly compare the transportation options. This study indicates that at the present time hybrid-electric vehicles, particularly those using diesel components, can achieve the highest efficiency among available technologies using natural gas as the primary energy source. Hydrogen spark ignition, all-electric battery-powered, and methanol fuel cell vehicles rank lowest in well-to-wheel efficiency because of their poor fuel production efficiencies.