In this paper, the mass transfer coefficients for trichloroethylene (TCE), toluene (TOL) and dimethyl sulfide (DMS) are experimentally determined for different porous and composite membranes. For polypropylene/polyvinylidenedifluoride porous layer/thin film polydimethylsiloxane dense layer composite membranes, membrane mass transfer coefficients are 2.55E-03, 2.82E-03 and 2.90E-03 m/s for TCE, TOL and DMS in N-2 at 30.0 +/- 0.1 degrees C, respectively. For polyester/polyacrylonitrile porous layer/thin film polydimethylsiloxane dense layer composite membranes, they are higher, namely 4.28E-03, 4.55E-03 and 4.81E-03 m/s for TCE, TOL and DMS in N-2 at 30.0 +/- 0.1 degrees C, respectively. Analysis of the contribution of the dense layer of both composite membranes to the total membrane resistance for mass transfer, showed that this contribution was small for both composite membranes. The higher mass transfer coefficients of the thin film polydimethylsiloxane composite membranes from this study in comparison to others from the literature are primarily due to improvement of the mass transfer characteristics of the porous layer. Analysis of the mass transfer characteristics of the different porous layers of which the total porous layer is composed, showed that the contribution of the porous "backing" layer for mechanical support can be substantial in comparison to the porous layer in contact with the dense layer. (c) 2008 Elsevier B.V. All rights reserved.