Pressure retarded osmosis (PRO) suffers Reverse Salt Diffusion (RSD) and concentration polarization (CP), which reduce its performance. The current work investigates the effect of the operating conditions (concentrations, solutions, pressures, flow rates, and temperatures) on RSD and, as a consequence, on the produced power. The results show that the salt diffusion is severely affected by the operating conditions, which should be carefully controlled to reduce the power losses in osmotic power plants based on PRO. The relationship between CP and RSD is also studied, showing how RSD aggravates the internal concentration polarization (ICP). (C) 2016 Elsevier B.V. All rights reserved.