Furnace oil is one of the cheapest fuels available for industrial use. It is a by-product of petroleum refineries. While processing the CRUDE Oil, FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD, Petrl, etc.

Furnace Oil is a fuel oil which is dark and viscous. Furnace oil is used mainly in different furnaces of the steel plant, in power plant boilers for raising steam and for injection in the blast furnace. It is also  sometimes used in air presenters. 

The furnaces which are used mainly for heating or pre-heating a large quantity of metal, are the main users of FO.