In the present study, transport mechanisms of various binary systems such as alcohol-hexane, alkane-hexane, lipid-hexane, and diesel fuel-kerosene systems through a PDMS-based dense membrane were investigated using a combined regular solution (RS) and solution-diffusion (SD) model at constant pressure and temperature. The combined model contains many important factors for permeability such as diffusivity, degree of swelling membrane, membrane thickness, and osmotic pressure. Total, hexane, and solvent fluxes (except for a part of the solvent flux) of all systems were controlled by molar volumes of hexane and solvent and solubility parameters of hexane, solvent, and membrane polymer based on the combined model. The selectivity of the solvent in these systems seems to depend upon the similarity of the molecular structures of hexane and solvent, corresponding to entropy mixing, and the interaction of the hexane-solvent-membrane polymer, corresponding to enthalpy mixing. The combined model could well describe the transport mechanism of the binary system. (C) 2011 Elsevier B.V. All rights reserved.