In petroleum refining, a relatively severe thermal cracking process designed to completely convert residual oils into gases, naphtha, gas-oil and coke. The gas-oil fraction is usually the major product obtained from coking, and is used primarily as catalytic cracker feedstock. The coke obtained from the process is usually consumed as fuel, although there are a number of specialized products made from coke, such as electrode raw material, chemicals and metallurgical coke. These latter products require further processing of the basic petroleum coke obtained from this process. There are several different coking processes employed commercially, including delayed coking, fluid coking and Fexicoking.