Petroleum is the single largest source of energy used in the United States. The nation uses two times more petroleum than either coal or natural gas and four times more than nuclear power or renewable energy sources. Before petroleum can be used it is sent to a refinery where it is physically, thermally, and chemically separated into fractions and then converted into finished products. About 90 percent of these products are fuels such as gasoline, aviation fuels, distillate and residual oil, liquefied petroleum gas (LPG), coke, and kerosene. Refineries also produce non-fuel products, including petrochemicals, asphalt, road oil, lubricants, solvents, and wax. Petrochemicals (ethylene, propylene, benzene, and others) are shipped to chemical plants, where they are used to manufacture chemicals and plastics. [DOE 1998]

The United States is the largest producer of refined petroleum products in the world, with 29 percent of global production and 155 operating refineries. In 1999 refineries supplied more than 6 billion barrels of finished products and employed about 64,000 people. [EIA 2000, DOC 1999] U.S. refineries are also the largest energy consumers in manufacturing and spend $5-$6 billion annually in pollution abatement costs. [MECS 1994, DOE 1998] The broad North American Industry Classification (NAICS) for refining is NAICS 324.