Installed capacity at Pennsylvania's electric power plants (utility and nonutility) in 1999 was 36.6 million kW, all of it privately owned. In the same year, total electricity generation was 195.6 billion kWh. In 2000, energy consumption was 390 million Btu (98.3 million kcal) per capita, ranking Pennsylvania 16th among the 50 states. Electric energy sales in the state in 1998 exceeded 127.5 billion kHz, of which 38% was industrial, 33% residential, and 29% commercial.
Pennsylvania's nuclear power production dropped abruptly on 28 March 1979, when a malfunction at the 906,000-kW Unit 2 plant operated by Metropolitan Edison (a subsidiary of General Public Utilities) at Three Mile Island near Harrisburg caused the reactor's containment building to fill up with radioactive water. Some radioactive steam was vented into the atmosphere, and thousands of residents of nearby areas were temporarily evacuated. A 12-member panel appointed by President Jimmy Carter to investigate the accident found serious flaws in the design of the plant's safety systems and in federal regulation of the nuclear power industry. Metropolitan Edison's 819,000-kW Unit I plant was also shut down after the accident but was reopened in fall 1985.
Operating nuclear plants in Pennsylvania as of 2001 were the Peach Bottom Units 2 and 3 (combined capacity 2,090,000 kW), 85% of which is owned jointly by Philadelphia Electric and Public Service Electric and Gas; Beaver Valley Units 1 and 2 (combined capacity 1,640,000 kW), at Shippingport, 69% owned by Duquesne Light and Ohio Edison; Susquehanna Units 1 and 2 (2,100,000 kW), 90% owned by Pennsylvania Power and Light; Limerick Units 1 and 2 (with capacities of 1,134,000 each) near Philadelphia; and Unit 1 of the Three Mile Island plant, with a capacity of 816,000 kW.
The nation's first oil well was struck in Titusville in 1859, and for the next five decades Pennsylvania led the nation in oil production. Reserves totaled 10 million barrels in 2001, and output dropped to 6,000 barrels per day in 2001. Marketed natural gas production in 2001 was 157 billion cu ft (4.44 million cu m); estimated reserves as of 2001 were 1,775 billion cu ft (50.3 billion cu m). Virtually all the state's commercial oil and gas reserves lie beneath the Allegheny High Plateau, in western Pennsylvania.
Coal is the state's most valuable mineral commodity, accounting for more than two-thirds of all mine income; the state's output in 1998 represented 7.2% of US production. In 2000, Pennsylvania's mining companies produced 74,619,000 tons of coal. Pennsylvania is the only major US producer of anthracite coal, with an output of 4,572,000 tons in 2000; bituminous coal production totaled 70,046,000 tons. Bituminous coal is mined in Washington, Clearfield, Greene, Cambria, Armstrong, Somerset, Clarion, Allegheny, and 19 other counties in the western part of the state; anthracite mining is concentrated in Schuylkill, Luzerne, Lackawanna, Northumberland, Carbon, Columbia, Sullivan, and Dauphin counties in the east. In 1998, there were 375 active coal mines, 97 underground and 278 surface. Recoverable reserves as of 2001 were 541 million tons of bituminous and 16 million tons of anthracite.