Serious energy and environmental issues are associated with transportation. The U.S . transportation sector remains almost entirely dependent on petroleum as an energy source and more than 50 percent of the petroleum used in the United States must now be imported. Petroleum use is responsible for most of the environmental problems resulting from transportation, including carbon dioxide emissions that may contribute to global climate change.
U.S. Petroleum Production and Consumption: 1970-99
Million barrels per day
Source: U.S. Department of Energy, Energy Information Admin istration, Annual Energy Review 1999 (Washington, DC: July 2000), Table 5.1.