petroleum coke is a solid that is mainly made of carbon. it is similar to coke, but it is gotten from petroleum (coke is made from coal). petroleum coke can be used as an industrial fuel, but there are very toxic by-products based on nickel and vanadium which make this a problem. petroleum coke is also used in the aluminum industry, and in the heat treatment of steel and iron. petroleum coke may be kept in a pile near an oil refinery ready for sale.