Fuel is material that can produce heat while being consumed, by burning, for example. Fossil fuels, also called mineral fuels, are combustible materials that are organic, having derived from remains of living beings. They include coal, lignite, natural gas, peat, and oil. Artificial fuels, such as gasoline and kerosene, are made from these natural fuels. Fossil fuels can take a number of forms: methane is a gas, oil a liquid, and coal a solid.
Some fossil fuels are referred to as carbonaceous fuels, which derive from plant waste. The carbonaceous fuel with the lowest carbon content is peat, which is estimated to cover about 2% of the Earth’s land in wetlands known variously as bogs, mire, moors, swamps, and peatlands. Fuel peat is different than moss peat, which is used in agriculture.
Lignite is the carbonaceous fuel with the next highest amount of carbon. Also called brown coal, is brownish or yellowish and has more moisture than coal. It is found in North America and Germany.
Coal, which has the highest carbon content, still has a range among its five types. They are, in increasing order, black lignite or subbituminous coal, bituminous coal, semibituminous coal, semianthracite, and anthracite. Note that semibituminous coal is high-grade bituminous coal, while semianthracite is low-grade anthracite coal. Of these, anthracite is most nearly pure carbon.
Natural gas is composed of gaseous hydrocarbons mixed with other components. Its main component is methane, which makes of 80–95% of its content. Other gases included may be butane, ethane, and propane. It is found both near deposits of petroleum, as well as separately.
Crude oil, or petroleum, is another of the fossil fuels. It is found in deposits in rock formations within the Earth and extracted for use as fuel oil, gasoline, and other products such as wax, manufacturing of plastics, lubricants, and sulfuric acid, among others. Saudi Arabia is both one of the largest producers and largest exporters of crude oil in the world.
In 2006, world energy consumption was 86% fossil fuels or their derivatives. This included 36.8% petroleum, 26.6% coal, and 22.9% natural gas. The remaining energy was supplied by non-fossil fuel such as hydroelectric, nuclear energy, geothermal energy, and energy generated by solar power, tides, and wind. World energy consumption rises yearly.
Because there is a finite amount of fossil fuels available, their depletion is a source of concern. The fact that these fuels release pollutants, such as carbon monoxide, when burned is another source of concern. The possibility that their burning contributes to global climate change or global warming has been the subject of heated debate.