Petroleum separation processes are intensive in exergy use. However, only a very small fraction of the consumed exergy is converted into products. Due to the significant magnitude difference between consumed exergy and processed exergy, as well as to the unknown molecular structure of the involved streams, the calculation of specific exergy and of exergy efficiency is a delicate topic that involves significant uncertainties. Comparison and explanation of five different ways to perform exergy evaluation of petroleum separation processes are conducted. The indication of advantages and disadvantages of each formulation is presented. The chemical and physical exergy calculation for petroleum and its fractions are covered. An application is performed and the results are discussed.