Petrochemistry is a branch of chemistry that studies the transformation of crude oil (petroleum) and natural gas into products or raw materials. These petrochemicals have become a major part of the chemical industry today.It may be possible to make petroleum from any kind of organic matter under suitable conditions. The concentration of organic matter is not very high in the original deposits, but petroleum and natural gas evolved in places that favored retention, such as sealed-off porous sandstones. Petroleum, produced over millions of years by natural changes in organic materials, accumulates beneath the earth's surface in extremely large quantities.

The first commercial oil well was set up in 1859, two years after which the first oil refinery was set up. The industry grew in the late 1940s. Demand for products from the petrochemical industry grew during the World War II. The demand for synthetic materials increased, and this rising demand was met by replacing costly and sometimes less efficient products with these synthetic materials. This caused petrochemical processing to develop into a major industry.

Before this, petrochemical industry was a tentative sector where various experiments could be carried out. The industry used basic materials: synthetic rubbers in the 1900s, Bakelite, the first petrochemical-derived plastic in 1907, the first petrochemical solvents in the 1920s, polystyrene in the 1930s.[citation needed] After that period, the industry produced materials for a large variety of areas—from household goods (kitchen appliances, textile, furniture) to medicine (heart pacemakers, transfusion bags), from leisure (running shoes, computers) to highly specialized fields like archaeology and crime detection.