A composite polydimethylsiloxane (PDMS)/polyamide (PA) membrane was synthesized and sorption, diffusion and permeation of C3H8, CH4 and H-2 were studied both in pure and mixed gas experiments. Pure gas experiments showed that, increasing transmembrane pressure increases solubility, permeability and diffusivity coefficients of heavier gases, C3H8, while does not affect or slightly decreases those of lighter ones, CH4 and H-2. Exactly opposite behavior was observed in mixed gas experiments (with the exception of C3H8 and CH4 solubility) due to the competitive sorption and diffusion in the plasticized polymer matrix. Temperature was realized to induce similar effects on permeation properties of pure and mixed gases. As expected, in rubbery membranes such as PDMS, permeability values of more condensable gases decrease with increasing temperature, whereas those of permanent gases increase. Parameters indicating linear pressure dependence (slopes m, n and q) and Van't Hoff-Arrhenius type temperature dependence (activation energies E-p, Delta H-s and E-d) of permeability, solubility and diffusivity coefficients in both pure and mixed gas experiments were estimated and discussed thoroughly. In the case of mixed gas experiments, increasing C3H8 concentration in the feed led to increasing solubilities, permeabilities and diffusivities of all the components due to the C3H8-induced swelling of the PDMS film. Experimental results demonstrated ability of the synthesized PDMS/PA membrane for separation of organic vapors from permanent gases. (C) 2009 Elsevier B.V. All rights reserved.