Bitumen is the impure, tar-like substance that is derived as a bi-product of the factional distillation of crude oil.
Bitumen is a naturally occurring viscous mixture, mainly of hydrocarbons heavier than pentane, that may contain sulphur compounds and that, in its natural occurring viscous state, is not recoverable at a commercial rate through a well.
Bitumen was used in antiquity as an adhesive, waterproofing agent, and mortar in construction. In the modern world its flexible, adhesive properties make it valuable as a key constituent of asphalt road surface material as well as 'tar paper' used in roofing.
Natural bitumen deposits known as 'tar sands' represent a major untapped petroleum resource. Research is ongoing into techniques to convert bitumen into synthetic crude oil at a cost that is competitive with other crude oil sources.