How it's made: Separated from natural gas liquids and from refinery gases by fractional distillation. It is rarely made on purpose, since both sources carry plenty of it.

How it's made: Separated from natural gas liquids and refinery streams by distillation, and made from n-butane by isomerization over a platinum catalyst on chlorided alumina. Refineries use it in alkylation units to make high-octane gasoline blendstock.