Coke is a solid carbonaceous residue derived from low-ash, low-sulfur bituminous coal from which the volatile constituents are driven off by baking in an oven without oxygen at temperatures as high as 1,000 C (2,000 F) so that the fixed carbon and residual ash are fused together. Coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. Coke from coal is grey, hard, and porous and has a heating value of 24.8 million Btu/ton (29.6 MJ/kg). Byproducts of this conversion of coal to coke include coal-tar, ammonia, light oils, and "coal-gas".
Petroleum coke is the solid residue obtained in oil refining, which resembles coke but contains too many impurities to be useful in metallurgical applications.

Petroleum coke is a carbonaceous solid derived from oil refinery cracking processes. Petroleum coke has many uses as a fuel, in the manufacture of dry cells, electrodes, etc. On the other hand, needle coke (aka "acicular coke") is a highly crystalline petroleum coke used in the production of electrodes for the steel and aluminum industries. Calcined Petroleum Coke also has its uses in Aluminium Industries .