| 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 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 [[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 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. |