In ejector refrigeration systems, the performance of the ejector is a crucial factor in determining the coefficient of performance, refrigeration power, component size and cost of the whole system. Most of the previously published mathematical models to predict the performance of ejectors consider ideal gas fluids. This paper presents a new approach which takes into account both ideal and real gases. The use of real gas equations of state enables considering either dry or wet vapor working fluids. For wet vapor ejectors, the choking phenomenon is analyzed considering a relaxation model for the calculation of the speed of sound in two-phase mixtures. The effectiveness of the model is verified by comparing the predicted results with experimental data available in the literature, using three different working fluids namely R141b, steam, and carbon dioxide. The results were found to be in good agreement with the experimental data and better than the estimations obtained applying previously published models. (C) 2012 Elsevier Ltd. All rights reserved.