Coal is the world's most abundant fossil fuel and it can supplement a significant part of our energy requirements far into the second millennium. Coal is a unique substance because it can provide energy and industrial products in all states of matter (solid, liquid, and gas). It is extracted as a solid through mining (Picture 1), exploited for it's gas content through coalbed methane development (Picture 2), and removed as a gas and liquid through surface and underground coal gasification processes (Picture 3). Coal can also act as the source rock and host of some "conventional" oil and gas reservoirs (Picture 4).
Coal is a combustible rock that has no fixed chemical formula. It is composed of varying quantities of carbon, hydrogen, oxygen, nitrogen, sulfur, and other substances (see Volume 2). The most common use of coal is for the generation of electricity (Picture 5).