Direct contact membrane distillation (DCMD) has a great potential for applications in many areas of separation processes. Usually, ill these processes, water constitutes a major component in fluid permeation, which is caused by the temperature difference between the feed and permeate. The transport models that are found in the literature in association with this process are often based on the Dusty-Gas model (DGM) for gas transport through porous media. These models' predictions are restricted to those cases in which only molecular diffusion and/or viscous flow contribute to the transport process. In this paper, a Monte Carlo simulation model is developed to study vapor permeation through membrane pores in association with DCMD. A three-dimensional network of interconnected cylindrical pores with a pore size distribution represents the porous membrane. The model takes also into account all molecular transport mechanisms based on the kinetic gas theory for a single cylindrical tube. The mechanisms are further dictated by the mean free path of permeating vapor molecules, by the size of the pores and by the operating conditions. Therefore. this model is comprehensive in its approach and can be applied to all forms of membrane distillation (MD) processes without resorting to any adjustable parameters. Model prediction(s) are in good qualitative agreement with available experimental data. (C) 2004 Elsevier B.V. All rights reserved.