There is no chemical formula for petroleum as it is not a chemical compound but a complex mixture that contains various amounts of different hydrocarbons and other chemicals. There are four main types of hydrocarbons generally found in petroleum, also known as crude oil: parrafins, aromatics, asphaltics and napthenes.
The chemical composition of petroleum can vary dramatically from one sample to another, although the specific concentrations of chemical elements in crude oil is generally quite standard. Most petroleum contains approximately 83 to 87 percent carbon, 10 to 14 percent hydrogen, 0.5 to 6 percent sulfur, 0.1 to 2 percent nitrogen and 0.5 to 1.5 percent oxygen. In addition, petroleum usually contains trace amounts of various metals.