In this study, we consider the case of a cogeneration unit installed within an oil refinery. This oil refinery has a processing capacity of 69,000 m3/day (433,996 barrels/day) of crude oil, and the generation system has the capacity to handle an electrical power of 97.8 MW and provide steam at a mass flow of 885 t/h. The cogeneration system has three conventional boilers, three heat recovery boilers connected to gas turbogenerators, two heat recovery boilers connected to a stream of carbon monoxide (CO) from the catalytic cracking units, three gas turbogenerators, three steam turbogenerators and one turboexpander. Using the Engineering Equation Solver (EES) and for each of the equipment units, we obtained an overview of mass, energy, entropy and exergy, in order to establish conciliation of the data removed from the refinery control data acquisition system (Plant Information - PI). Through internal routine procedures, we evaluated the most important parameters of performance, such as: energetic efficiency, exergetic efficiency, and irreversibility of equipment and of the complex as a whole. The results show that processes that have combustion phenomena as their structural elements present higher levels of irreversibility and of generation of entropy. In this regard, analysis based on aspects of the First Law shows, by way of example, that boilers reach efficiency levels of over 85%, while from the exergetic perspective these values tend to cluster around the 40% threshold. Finally, we discussed performance parameters different from those traditionally used in exergetic analyses, so that the technique may gain presence in industrial environments.