Lexikon

a general term applied to oil used for the production of power or heat. In a more restricted sense, it is applied to any petroleum product that is used as boiler fuel or in industrial furnaces. These oils are normally residues, but blends of distillates and residues are also used as fuel oil. Nowadays their use is restricted partly because of their high sulfur content partly because of the more economic natural gas. They are transformed into engine fuel or other products by hydrocracking, coking, etc.