The hybrid FO/RO desalination is an innovative technology which provides many advantages such as reducing RO fouling and scaling, recovery of osmotic energy of RO brine and minimizing the use of chemicals required for conventional pretreatment steps. Conceptual FO-RO system design alternatives were presented in this paper. Either seawater or RO brine may be used as a draw solution to extract water from an impaired source through FO. An analysis of osmotic energy recovery in this system was given and the main operating parameters and relationships governing the operation of the conceptual system were also described. At concentration gradients of 15 g/l and 30 g/l, the osmotic energy recovered ranged between 1.1 kJ and 2.2 kJ per each liter of permeate water, respectively. The power density of the membrane at these concentrations was 1.45 and 4.35 W/m(2), respectively. Future success of FO desalination depends on designing new membranes in terms of structure and configuration specifically tailored for FO. Four new membrane module configurations were suggested and described in this paper. The new configurations were intended to improve performance of the modules in terms of water flux and effectiveness of backwashing as well as to lower pressure drop in the membrane envelope. (C) 2010 Elsevier B.V. All rights reserved.