Oil is not a pure substance, it is a mixture. Petroleum, also known as crude oil , contains gasoline , kerosene , diesel oil , lubricating oil and other substances, which belong to mixtures. Petroleum contains mainly two elements: carbon and hydrogen. Oil refining is a physical change. Petroleum is separated according to the boiling point of each component and is mainly used as fuel oil and gasoline.
There are two theories about the oil-forming mechanism of petroleum: biological sedimentary oil and petrochemical oil. The former is widely accepted, that oil is formed by long-term evolution of organisms in ancient oceans or lakes, and belongs to biological deposits to form oil, which is non-renewable; the latter believes that oil is generated from carbon in the crust, and carbon has nothing to do with organisms. Renewable. Petroleum is mainly used as fuel and gasoline, and is also the raw material for many chemical industry products, such as solutions, fertilizers, pesticides and plastics.