This study demonstrates the application of the solution-diffusion pore-flow fluid-resistance (SDPFFR) model, which is used to describe solvent transfer in pressure-driven membrane separation processes. The experimental work is carried out in a reverse osmosis (RO) setup by using two different membranes, TFC-HR and TFC-ULP, manufactured by Koch Membranes Systems, Inc. (USA). Characterization for these membranes by using the transmission electron microscopy (TEM) is also presented. Aqueous solutions of sodium chloride and ammonium bicarbonate were used as feed at 15, 25, and 35 degrees C. The results show that water transfer in the feed side of the membrane is controlled by the molecular properties of the solute in addition to the operational conditions. Water permeability in the feed solution has been observed to increase as the solute hydration strength or concentration decrease, and as the temperature and the hydraulic pressure increase. The validated model explains the interaction between water permeability in the feed solution and water permeability inside the membrane material. The model shows good agreement with the experimental results. It provides good description for solvent transfer in membrane separation processes and may be useful for future development and design applications, when based on experimental data. (C) 2010 Elsevier B.V. All rights reserved.