A Monte Carlo simulation model is developed to study vapor flux through hydrophobic membranes in association with direct contact membrane distillation (DCMD) process. The porous membrane is represented by a three-dimensional network model of inter-connected cylindrical pores with distributive effective pore sizes. Vapor flux through membrane pores is described by gas transport mechanisms founded on the kinetic theory of gases for a single cylindrical pore. This model can take into consideration the effects of temperature polarization phenomenon, porous membrane physical properties, including membrane pores inter-connectivity (topology), process dynamics, and apply them into the prediction of process vapor flux (permeability) and the description of MD transporting process. The model can simultaneously solve for the MD processes vapor flux and membrane effective surface temperatures, contrary to other models in which one of them has to be given in order to solve for the other. We argue that this Monte Carlo simulation model can adequately describe MD processes transport phenomenon and predicts process vapor flux without resorting to any adjustable parameters. It is comprehensive in its approach; and it can be applied to all configurations of MD processes published in the literature. The results obtained, in general, show an excellent qualitative agreement with available experimental data. (c) 2005 Elsevier B.V. All rights reserved.