has role composed primarily of alkane aromatic compound cyclic hydrocarbon fossil fuel fuel oil furnace oil An oil which 1) is liquid at room temperature (approximately 20 degrees Celsius) 2) is intended to be burned in a furnace or boiler for the generation of heat or used in an engine for the generation of power, 3) is obtained from petroleum distillation, either as a distillate or a residue, 4) composed of long hydrocarbon chains, particularly alkanes, cycloalkanes and aromatics. heavy oil Oils having a flash point of approximately 42 degrees Celsius and oils burned in cotton or wool-wick burners are not typically considered fuel oils. The term fuel oil is also used in a stricter sense to refer only to the heaviest commercial fuel that can be obtained from crude oil, i.e., heavier than gasoline and naphtha. marine fuel oil