A typical humidification dehumidification desalination (HDH) system operates at ambient pressure. However, the current work presents an HDH system that works at different pressures iii order to improve its performance. The system parameters are optimized to maximize the Gain Output Ratio (GOR). In addition, the effect of the mass ratio, pressure ratio, effectiveness of components, and the maximum temperature of the system is studied. It is found that for an effectiveness of 0.8 and humidifier pressure of 50 kPa, a maximum GOR of 3.8 is obtained at a pressure ratio of 133 (GOR value of 8.2 is obtained for the effectiveness of 0.9). Sensitivity analysis is also performed to determine the main parameters that affect the system performance. It has been found that GOR is more sensitive to the pressures of humidifier and dehumidifier (32% contribution bf pressure on the GOR among the variables considered). In addition, an exergy analysis is performed to determine the parameters that result in higher exergy destruction in the system. It is found that increasing the pressure ratio increases the irreversibility while maximum temperature has no effect on exergy destruction up to 60 C. (C)2017 Elsevier B.V. All rights reserved.