The unrelenting increase in the consumption of oil in the US light-duty vehicle fleet (cars and light trucks) presents an extremely challenging energy and environmental problem. A variety of propulsion technologies and fuels have the promise to reduce petroleum use and greenhouse gas emissions from motor vehicles. Even so, achieving a noticeable reduction on both fronts in the near term will require rapid penetration of these technologies into the vehicle fleet, and not all alternatives can meet both objectives simultaneously. Placing a much greater emphasis on reducing fuel consumption rather than improving vehicle performance can greatly reduce the required market penetration rates. Addressing the vehicle performance-size-fuel consumption trade-off should be the priority for policymakers rather than promoting specific vehicle technologies and fuels. (C) 2008 Elsevier Ltd. All rights reserved.