Bitumen, also called asphalt, is a black, gummy substance composed of hydrocarbons. It can occur naturally (sometimes called crude bitumen), accumulating in deposits formed from the remains of once-living organisms subject to intense heat and pressure under the earth’s surface (as in Los Angeles’s La Brea Tar Bits or Alberta’s Athabasca oil sands). Its more common form, manufactured bitumen, is a residue remaining after the distillation of petroleum (see Roy).