During the last two decades the use of supported liquid membranes (SLMs) has been widely studied as an attractive alternative in gas separation processes. In this work supported ionic liquid membranes were used for propane/propylene gas mixtures separation using AgBF4 dissolved in BMImBF(4) as carrier solution. Gas permeation experiments were carried out with pure gases and with a 50:50 C3H8/C3H6 gas mixtures as feed gas under different operational conditions in order to study the influence of the different variables such as the transmembrane pressure, sweep gas flow rate and silver concentration in the membrane. It was found that under the similar operation conditions the permeability of the gaseous components in mixed gas experiments was about 6.1% lower for propane and 15% higher for propylene than in pure gas experiments. Moreover, it was observed that although the flux of propane was almost not affected by changes in the sweep gas flow rate, the flux of propylene increases reaching asymptotically a maximum value as the sweep gas flow rate was increased. With regard to the concentration of silver cations in the membrane it has no influence on the flux of propane, however the flux of propylene increased following a linear trend when the silver concentration in the membrane was increased from 0 to 1 M. High permeabilities and selectivities up to 20 were obtained, so Ag+-SILMs systems are suitable to separate C3H8/C3H6 gas mixtures since it is possible to obtain a permeate stream with a purity of propylene high enough to be used in most of the applications of propylene. Finally, the performance of the system was tested at longer times and it was observed that although the ionic liquid membranes seems to be stable, the flux of propylene started to decrease after 90 min of operating time because the silver cations began to be reduced to metallic silver. For this reason further research in order to avoid, or at least minimize the reduction of the silver cations is needed. (C) 2012 Elsevier B.V. All rights reserved.