This course is aimed at third-year engineering students specializing in Petroleum Engineering. It constitutes a summarized synthesis of some works collected from several books (see bibliographical references) allowing for the provision of technical and scientific knowledge on the chemical composition of petroleum, as well as the classification of petroleum products, it also provides knowledge on refining processes and their main products and their physicochemical characteristics. Thus, environmental constraints and the evolution of refining are also detailed , also several analysis methods, Finally, some examples of petrochemical processes (PVC and ammonia) are presented.