Illinois is one of the nation's leading energy producers and consumers. Electric power production (utility and nonutility) totaled 163.6 billion kWh (5th in the US) in 1999; total installed capacity was 34.3 million kW, nearly all of it privately owned. In 2000 Illinois's total per capita energy consumption was 356 million Btu (89.7 million kcal), ranking it 22nd among the 50 states. Commonwealth Edison and Northern Illinois Light and Power are the largest suppliers. Coal-fired plants account for about 45% of the state's power production; nuclear power is also important, particularly for the generation of electricity in the Chicago area. The state's five operating nuclear power plants in 2001 (with 11 reactors) were all owned by Commonwealth Edison.
In 2000, Illinois ranked 3rd nationally in liquefied natural gas consumption, with 2.3 million gal (8.7 million l) per day delivered to over 3.7 million customers. People's Gas, a diversified energy conglomerate based in Chicago, is the largest firm. Marketed gas production in 2001 was 185 million cu ft (5.23 million cu m). Petroleum production, though steadily declining, totaled 33,000 barrels per day in 2002; reserves were 92 million barrels in 2001.
Illinois ranked 7th in the US in coal production in 1998, with 39.7 million tons; production declined to 33.4 tons in 1999. Recoverable reserves were estimated at 819 million tons in 2001. Coal is abundant throughout the state, with the largest mines in the south and central regions. Coal mining reached its peak in the 1920s, but suffered thereafter from high pricing policies, the depression of the 1930s, and the environmental restrictions against burning high-sulfur coal in the 1970s. In 1998 there were 24 productive coal mines—8 surface (strip) mines and 16 underground mines.