What is the nature and classification of crude oil and crude oil?

Petroleum is a complex mixture of various hydrocarbons and non-hydrocarbon compounds. The nature of oil contains both physical and chemical properties. Physical properties include color, density, viscosity, freezing point, solubility, calorific value, fluorescence, optical activity; chemical properties include chemical composition, composition and composition of impurities and so on. The relative density of crude oil generally between 0.75 to 0.95, a few greater than 0.95 or less than 0.75, the relative density of 0.9 to 1.0 known as heavy crude oil, less than 0.9 is called light crude oil.