A thin layer of silicone oil was immobilized in part of the micropores of the polypropylene hollow fiber substrate beneath the plasma-polymerized polydimethylsiloxane (PDMS) skin on the outer surface of the hollow fiber. Such a liquid in the hollow fiber membrane was used to study the separation properties for the following volatile organic compound (VOC)-containing systems: toluene-N-2, methanol-N-2, acetone-N-2. The observed benefits of having the thin immobilized liquid membrane (ILM) incorporated in the microporous structure were, 2-5 times more VOC-enriched permeate since the nitrogen flux was drastically reduced and the separation factor was 5-20 times increased depending on the type of the VOC and the feed gas flow rate. The stability of such a thin ILM-based hollow fibers membrane was studied over an extended period of time (six months to two years). The stable results demonstrated the potential utility of such an ILM-based hollow fiber device for VOC-N-2/air separation. A mathematical model was also developed for VOC-N-2 permeation-separation in a hollow fiber permeator having this special type of membrane containing a thin ILM. Experimental results were compared with the results obtained by numerically simulating the mathematical model of the permeator. The values of various parameters used for the simulations were experimentally determined. The VOC outlet concentrations for all VOC-N-2 systems were well anticipated by the model simulations. (C) 2003 Elsevier Science B.V. All rights reserved.