Petro chemistry is the branch of chemistry that deals with petrochemicals. Petrochemicals are the chemicals that are obtained during the process of petroleum refining. It can also be stated as the study of transformation of natural gas and crude oil into raw materials that can be used in the production of petro chemicals. Crude oil is the chief raw material for the production of petro chemicals. The composition of crude oil consists of many different hydrocarbons. The average composition includes 84% carbon,14% hydrogen,1-3%nitrogen oxygen,metals,salts. Some petrochemicals can also be obtained by natural resources such as maize, natural gas coal etc. there are two major classes of petro chemistry i.e. olefins and aromatics.