Also called butene, any of four isomeric compounds belonging to the series of olefinic hydrocarbons. They are formed during the cracking of petroleum to produce gasoline; they can also be prepared commercially by the catalytic dehydrogenation of butanes. The major part of the butenes is utilised for the production of octanes, which are important constituents of gasoline. On dehydrogenation, normal butenes form butadiene, the principal starting material for synthetic rubber.