The osmotically driven membrane process, such as pressure-retarded osmosis (PRO) or forward osmosis (FO), assisted reverse osmosis (RO) hybrid systems are investigated for low-energy cost seawater desalination and wastewater treatment, and the simultaneous RO brine (or RO concentrates) management. Unlike the earlier studies, the hollow fiber types of modules are used in these hybrid systems. For commercialization of the hybrid systems, a big concern is that how much energy per unit product (i.e., specific energy) can be saved due to the hybrid systems as compared to the most preferred conventional RO technique. For this, the generalized mathematical models for an axial-flow and a radial-flow hollow fiber module are developed in the current study. These models are applicable to evaluate all PRO, FO, and RO processes. For an RO recovery of 50% and FO/PRO dilution of 40%, itis found that around 25% specific energy saving may be realized in both the hybrid systems as compared to the conventional RO system at studied operating conditions. Interestingly, the results also reveal that as the RO recovery increases, the specific energy saving increases for the FO-RU hybrid system but decreases for the RO-PRO hybrid system. (C) 2017 Elsevier B.V. All rights reserved.