Although coal deposits exist in nearly every region of the world, commercially significant coal resources occur only in Europe, Asia, Australia, and North America. Commercially significant coal deposits occur in sedimentary rock basins [3], typically sandwiched as layers called beds or seams [4] between layers of sandstone [5] and shale [6]. When experts develop estimates of the world��s coal supply, they distinguish between coal reserves and resources. Reserves are coal deposits that can be mined profitably with existing technology��that is, with current equipment and methods. Resources are an estimate of the world��s total coal deposits, regardless of whether the deposits are commercially accessible. Exploration [7] geologists [8] have found and mapped the world��s most extensive coal beds. At the beginning of 2001, global coal reserves were estimated at 984.2 billion metric tons, in which 1 metric ton [9] equals 1,016 kg (2,240 lb). These reserves occurred in the following regions by order of importance: the Asia Pacific, including Australia, 29.7 percent; North America, 26.1 percent; Russia and the countries of the former Union of Soviet Socialist Republics (USSR), 23.4 percent; Europe, excluding the former USSR, 12.4 percent; Africa and the Middle East, 6.2 percent; and South and Central America, 2.2 percent.

Coal deposits in the United Kingdom, which led the world in coal production until the 20th century, extend throughout parts of England, Wales, and southern Scotland. Coalfields in western Europe underlie the Saar and Ruhr valleys in Germany, the Alsace region of France, and areas of Belgium. Coalfields [10] in central Europe extend throughout parts of Poland, the Czech Republic, and Hungary. The most extensive and valuable coalfield in eastern Europe is the Donets Basin, between the Dnieper and Donrivers (in parts of Russia and Ukraine). Large coal deposits in Russia are being mined in the Kuznetsk Basin in southern Siberia. Coalfields underlying northwestern China are among the largest in the world. Mining of these fields began in the 20th century.

United States coal reserves are located in six major regions, three of which produce the majority of domestically [11] mined coal. The most productive region [12] in the United States is the Appalachian Basin, covering parts of Pennsylvania, West Virginia, Kentucky, Tennessee, Ohio, and Alabama. Large quantities of coal have also been produced by both the Illinois Basin��extending through Illinois, Indiana, and Kentucky��and the Western Interior Region��extending through Missouri, Kansas, and Oklahoma. Other commercially important U.S. coal regions include the Powder River Basin, underlying parts of Montana and Wyoming; the Green River Basin in Wyoming; the Uinta Basin, covering areas of Utah and Colorado; and the San Juan Basin, underlying parts of Utah, New Mexico and Colorado.

In 2001 estimates of total U.S. coal reserves were approximately 246 billion metric tons. A

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