FCC feedstock is a heavy fraction of crude oil distilled through distillation of crude oil (or other petroleum refining processes), or mixed with a small amount of residue in heavy distillate oil, or deasphalting residue after deasphalting by solvent, or all using normal pressure residuum or vacuum residue. In the process of reaction, the non volatile carbon like substances are deposited on the catalyst and condensed into coke, which reduces the activity of the catalyst. It needs to be burned with air (see catalyst regeneration) to restore the catalytic activity and provide the heat needed for the cracking reaction. Catalytic cracking is one of the main processes of producing gasoline from heavy oil in an oil refinery. The octane number of the gasoline is high (about 80 of the motor method), and the cracking gas (a refinery gas) contains more propylene, butene and isomeric hydrocarbons.