Furnace oil (fuel oil, FO) is a residual fuel (motor spirit / gasoline, high speed diesel and kerosene are distillate fuels). It is a dark, viscous liquid at room temperature. It is a complex mix of hydrocarbons with carbon atoms ranging mainly from 20 to 55.

Used as fuel for Power Generation in DG Sets, boilers, furnaces, air preheater, bunkering etc.