Changes

[[file:Coal_Bituminous.jpg|thumb|300px|Coal. [http://geosurvey.state.co.us/energy/Coal/Pages/Whatisit.aspx Courtesy Colorado Geological Survey].]]

[[file:Coal_Bituminous.jpg|thumb|300px|Coal. [http://geosurvey.state.co.us/energy/Coal/Pages/Whatisit.aspx Courtesy Colorado Geological Survey].]]

Although [[oil as an energy source|oil]] is, at present, the principal source of energy in the world (easier to produce, transport, store, and use) and [[natural gas|gas]] is acclaimed as the fuel of the future because it is the cleanest burning of the main sources of energy, coal is, by far, the most abundant and lowest cost [https://www.udemy.com/blog/types-of-fossil-fuels/ fossil fuel] source of energy; coal reserves are 5 times as large as either oil or gas reserves, and coal resources are estimated to be about 17 times the oil resources and 20 times the gas resources.

Although [[oil as an energy source|oil]] is, at present, the principal source of energy in the world (easier to produce, transport, store, and use) and [http://www.glossary.oilfield.slb.com/en/Terms/n/natural_gas.aspx gas] is acclaimed as the fuel of the future because it is the cleanest burning of the main sources of energy, coal is, by far, the most abundant and lowest cost [https://www.udemy.com/blog/types-of-fossil-fuels/ fossil fuel] source of energy; coal reserves are 5 times as large as either oil or gas reserves, and coal resources are estimated to be about 17 times the oil resources and 20 times the gas resources.

[[file:St54Figure36.JPG|thumb|300px|Coal production.<ref name=Salvador_2005>Salvador, Amos, 2005, Energy-A historical perspective and 21st Century forecast: AAPG Studies in Geology 54, 208 p.</ref>]]

[[file:St54Figure36.JPG|thumb|300px|Coal production.<ref name=Salvador_2005>Salvador, Amos, 2005, Energy-A historical perspective and 21st Century forecast: AAPG Studies in Geology 54, 208 p.</ref>]]