because it contains constituents of hydrocarbon compounds after it has been refined. Crude oil is refined to various organic compounds such as Kerosene,Petroleum gases,Dielsel oil ,Gas oil,Petroleum ethers and ligroin,Lubricating oils,Bitumen and Residues e.t.c with the inceptive use of fractional distillation at various temperatures .Thereby depicting Crude oil as a mixture of hydrocarbon compounds.Take care