In this study, the integration of different desalination systems into cogeneration systems has been examined. Based on the operating conditions of the cogeneration system, this integration can result in either the improvement or impairment of the cogeneration efficiency. The R-curve is a powerful tool to investigate the effect of this integration on the cogeneration system performance. Several scenarios for integration of RO and MED systems at different operating points are investigated. Some case studies are examined using the presented concept to verify the proposed methodology. There is a significant variation in the economics of the systems in the presented integration scenarios. The R-curve has been utilized for the integration of MED and RO desalination technologies with cogeneration systems to identify effective ways to decrease the operating cost. As an illustration, based on the operating conditions, the integration of a 24 MW RO desalination plant can either provide a 12.123 MW fuel saving or cause 23.502 MW excess fuel consumption due to different cogeneration performances in the same cogeneration system (case study 1). Also, the integration of 17.8 MW(t) MED unit can either cause 47.835 MW excess fuel consumption or provide 28.974 MW fuel saving (case study 2).