The performance of the osmotic-pressure RO, FO and PRO processes is analyzed on the basis of a uniformed model with water flux derived from the modified conventional expression J(w) = beta * A * (Delta pi - Delta p) where beta (<1.0) stands for the FO actual/ideal flux ratio of a given membrane in a defined salinity gradient and also applies to PRO; whereas beta = 1.0 applies to RO membranes. The beta parameter takes account of the detrimental effects on flux in FO and PRO membranes and becomes unity for RO membranes. The uniformed model is explored to evaluate the various aspects of RO, FO and PRO and some of their FO-RO and PRO-RO hybrids, with emphasis on advanced closed circuit desalination RO (CCD) and PRO (CC-PRO) techniques and widespread feed sources such as treated sewage effluent (TSE) and seawater (SW) or seawater brine (SWB) from SWRO desalination plants. The results of this comparative study reveal that the desalination of SW and TSE with CCD proceeds with low energy of near absolute energy conversion efficiency at the ultimate state-of-the-art, unattainable by the conventional techniques practiced today. With regard to FO and PRO, this comparative study reveals that the effectiveness of both processes depends on the actual/ideal flux ratio (beta) which manifests membranes' detrimental effects. Moreover, this study also shows that PRO power generation is also a function of the permeation/draw flow ratio (delta) apart from beta and the salinity gradient and that operating at high delta (e.g., 40) of high power density (PD) yields low net electric power density (NEPD) which takes into account the power consumption of the auxiliary components in the PRO system. The distinction between PD and NEPD considered in the context of the SW SE and SWB-TSE salinity gradients suggests that such applications are unlikely to become economically effective for energy generation and the same conclusion is also true for the application of the FO-RO and PRO-RO hybrids for the desalination of TSE which proceeds most effectively by direct CCD with exceptionally high recovery and low energy. (C) 2016 Published by Elsevier B.V.