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Petroleum is called black gold because when crude oil is extracted from the land it is black in color and it is a very valuable fossil fuel. Petroleum is used for running machinery, transport vehicles, airplanes, etc. It is also used to produce a variety of products like diesel, kerosene, wax, lubricants, etc. Petroleum is a non renewable source of energy and its reserves are limited. Thus, petroleum is a very precious natural resource in the absence of which the human economic growth will suffer a huge loss.