Fuel oil or
heavy oil is a
fraction obtained from
petroleum distillation, either as a distillate or a residue. Broadly speaking, fuel oil is any liquid fuel that is burned in a
furnace or
boiler for the generation of heat or used in an
engine for the generation of power, except oils having a
flash point of approximately and oils burned in cotton or wool-wick burners. In this sense,
diesel is a type of fuel oil. Fuel oil is made of long
hydrocarbon chains, particularly
alkanes,
cycloalkanes and
aromatics. 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.