This chapter is a review of petroleum chemistry particularly as it relates to oil spills. The traditional separation of saturates, aromatics, resins, and asphaltenes (SARA) oil components is summarized. Details on these groupings and many compounds within the groupings and, where available, the typical amounts found in some oils are given. A detailed look at compounds found in oil and the amount of these is presented. The compounds are related to the overall composition and the SARA composition. Details of more than 500 compounds will be given in the chapter.