A refining process in which heat and pressure are used to break down, rearrange, or combine hydrocarbon molecules. Thermal-cracking includes gas oil, visbreaking, fluid coking, delayed coking, and other thermal cracking processes (e.g., flexicoking).

the breaking up of large molecules into smaller ones by the use of high temperature. (see cracking)

One type of cracking in the refining process. Gas oils obtained in the topping process are subject to extreme temperatures under severe pressure. In the process, gas-oil molecules are cracked and broken into new molecules. From the high boiling gas-oil fraction, a fraction is broken off consisting of light hydrocarbons having the low boiling range of gasoline. A heavy, high-boiling residue of the cracking process finds its way into the market as heavy industrial fuel oils.