A liquid state of petroleum hydrocarbons composed of different organic compounds characterized by different molecular weight, size, shape, solubility, and elemental composition such as alkanes, naphthenes, and aromatics; while the most
important non-hydrocarbon components are resins and asphaltenes. Crude oil is classified into different fractions according to molecular weight and the boiling point ; Gasoline from C5 to C10, Kerosene from C11 to C13, Light gas oil from C14 to C18, Heavy gas oil from C19 to C25, Lubricating oil from C26 to C40, and residuum for > C40.