Advanced vehicles with lower emissions or higher fuel economy cannot accomplish these social goals unless consumers choose to purchase them instead of conventional automobiles. What attributes will these advanced vehicles need in order to have significant market penetration? In this paper we investigate the importance of “vehicle comparability” in comparative analyses of conventional and alternative fuel/powertrain automobiles. Comparability can mean that the vehicles have identical power, size, safety, range, etc. Alternatively, it can mean that customers find the bundle of attributes of a vehicle equally attractive to the bundle of attributes of another. If customers insist on current vehicle attributes, the advanced vehicles will not be attractive. Analysts differ in the extent to which they account for vehicle equivalency.