This paper presents the exergy analysis of petroleum separation processes that take place in offshore platforms, in order to characterize the thermodynamic performance of these processes and identify possible ways of increasing the overall performance of the platform. In offshore platforms petroleum is separated into water, oil and gas. After the separation, water is sent back to the sea or reinjected into the reservoir, oil is pumped and gas is compressed and sent to the refineries. Gas-turbines and furnaces are employed to generate electricity, mechanical power and hot water that are utilized in the platform. These equipment consume part of the natural gas produced by the platform. The exergy analysis developed for the offshore platform evaluates the exergy efficiency and the exergy destroyed in each set of equipment (separators, pumps, compressors, furnaces and gas-turbines), as well as the overall platform performance. The importance of each set of equipment in the overall efficiency is quantified by the use of the factor f, defined as the relation between the consumed exergy in a particular set of equipment and the consumed exergy in the platform. This analysis is employed to evaluate the performance of a typical Brazilian offshore platform.