Cracking.

In the petroleum industry, cracking refers to the chemical conversion process following the distillation of crude oil, by which fractions and residue with long-chain hydrocarbon molecules are broken down into short-chain hydrocarbons. Cracking is accomplished under pressure by thermal or catalytic means and by injecting extra hydrogen. Cracking is done because short-chain hydrocarbons, such as gasoline, diesel, and jet fuel, are more commercially valuable than long-chain hydrocarbons, such as fuel and bunker oil. Steam cracking of light gases or light naphtha is used in the petrochemical industry to obtain lighter alkenes, which are important petrochemical raw products.