Energy use is associated with environmental problems and other externalities arising from personal transportation. In this article, we review trends in the use of the car and other modes of personal transportation in 10 OECD countries from 1970 to 1992. We analyze changes in energy use for these activities and discuss underlying components of, and causes for, these changes. We compare differences between the United States and the European countries studied, concluding that most of the variations arise because of differences in total transport activity and modal choice, not because of the energy efficiency of each mode. We analyze more closely differences in activity, which is dominated by the automobile, relating automobile use to differences in fuel prices and car taxation, in patterns of mobility, in demographic patterns, and in geographical factors like land use or place of residence. We conclude with a focus on one externality of transportation, the carbon dioxide emissions from travel. We note that these emissions are rising in all the countries studied. We suggest that policies aimed at stemming this rise must be integrated with other policies related to other problems of transportation, many of which are perceived to be more important than that of CO2 alone.