Old miner at Baltimore tunnel, 51 years of service c. 1921; Pennsylvania Anthracite Heritage Museum Archives, Horgan#22439. photo: John Horgan Jr.Coal is a nonrenewable fossil fuel produced worldwide. It is formed when millions of years of pressure and heat turn the remains of prehistoric forests and swamps into coal. Coal is taken out of the earth either by deep mining (tunneling underground) or strip mining (digging out layers of earth). It exists in different grades or qualities.

Coal is used predominantly to produce electricity and to provide fuel for industries that require large amounts of heat. Production of steel, cement, and paper all rely on this industry. Coal traditionally has been used for heating many homes and businesses.

A quarter of the earth's coal reserves exists within the U.S. The American supply of coal potentially contains more energy than all of the remaining oil supplies around the world.

Pennsylvania is a major producer of two different grades of coal. Anthracite coal, also known as hard coal, is mined almost exclusively from northeastern Pennsylvania. Bituminous coal, a softer coal compared to anthracite, is found in western Pennsylvania, dominates the coal market, and is used in electricity generation.

In total, Pennsylvania ranks fourth within the country in coal production, producing roughly 6% of the nation's coal supplies in 2005. The importance of this industry is evident since coal produces nearly 40% of electricity generated nationally and 50% of Pennsylvania's electricity. Nearly half of the state's coal production is sold out of state to other areas needing the product.