High Quality Content by WIKIPEDIA articles! Butene, also known as butylene, is an alkene with the formula C4H8. It is a colourless gas that is present in crude oil as a minor constituent in quantities that are too small for viable extraction. It is therefore obtained by catalytic cracking of long chain hydrocarbons left during refining of crude oil. Cracking produces a mixture of products and the butene is extracted from this by fractional distillation.