Cokeis a fuel with few impurities and a highcarboncontent, usually made fromcoal. It is the solidcarbonaceousmaterial derived from destructive distillationof low-ash, low-sulfurbituminous coal. Cokes made from coal are grey, hard, andporous. While coke can be formed naturally, the commonly used form is man-made. The form known aspetroleum coke, or pet coke, is derived from oil refinery coker units or other cracking processes.