Based on the dusty gas model, expressions of the water vapor transfer coefficient of hydrophobic membranes were obtained. These expressions, together with data of air-liquid displacement measurements, constitute an independent method of determining the vapor transfer coefficient of hydrophobic membranes, which is required for predicting and simulating membrane distillation (MD) performance. As a test, this method was applied to three commercial hydrophobic membranes and the predicted transfer coefficient values agreed well with the values obtained from other methods employed in MD literature. The availability of an independent method of determining vapor transfer coefficient of the membrane makes it possible to validate MD models with greater certainty. (C) 2003 Elsevier Science B.V. All rights reserved.