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A synthetic fuel (or synfuel) is a fuel in liquid or gas form that can be manufactured. Synfuels have long been made from coal. Oil extracted from shale or tar sands is also sometimes called synfuel. Fuels can also be made from non-food crops.
Tar sands are a combination of sand and a thick oil called bitumen. This, along with oil shale, which is a layer of rock riddled with hydrocarbons in the form of kerogen, can be heated with steam to remove the crude oil in the two substances. Like oil, it must be refined before being put to use.