Exergy analysis is used as a tool for the evaluation of exergy losses in a two-phase steam–water injector in an effort to improve its overall performance in respect to exit pressure. The aim of this paper is to study irreversible losses in the component parts of the injector, including the steam nozzle, water nozzle and diffuser as well as the two-phase region comprising the mixing chamber and the condensation shock wave. Calculations based on experimental data revealed the regions with the greatest irreversibilities, namely in the two-phase region and in the steam nozzle. Particular attention was paid to the steam nozzle, for which a procedure was developed to determine the overall velocity coefficient, including all irreversibilities in the steam nozzle during steam expansion. The study indicated the most important factors influencing the injector’s performance. Finally, the exergy efficiency was calculated for the two investigated steam injectors.