Facilitated olefin transport membranes consisting of AgBF4 dissolved in poly(2-ethyl-2-oxazoline) (POZ) were prepared for use in propylene/propane separation. It was found that facilitated propylene transport through these membranes depends on their thickness. As the membrane thickness increases, the propylene permeability increases whereas the propane permeability remains almost constant, resulting in an increase in the membranes' selectivity of propylene over propane. The concentration fluctuation model for facilitated transport in the solid state predicts a dependence of facilitated transport on thickness. In this note, we compare the dependence of the propylene permeability of POZ/AgBF4 membranes on their thickness with that predicted by the concentration fluctuation model. (C) 2004 Elsevier B.V All rights reserved.