A simplified model was used to predict the performance of hollow fiber RO membranes. The model is based on the solution-diffusion membrane mass transport model and takes into account the effect of the pressure drop in the fiber bore and in the fiber bundle, the variation of the bulk solution concentration on the shell side of the fiber bundle and the concentration polarization. The results of the model showed reasonable agreements with the experimental data for B9 membranes and the data from an industrial RO plant based on B10 membranes.