The present work expands previous modeling knowledge on facilitated transport membranes for olefin/paraffin separation. A new robust and practical mathematical model for the description of light olefin flux in composite polymer/ionic liquid/Ag+ membranes is reported. The model takes into account three different transport mechanisms, i.e., solution-diffusion, fixed-site carrier and mobile carrier transport mechanisms. Fixed-site carrier contribution that appears thanks to the bounding of silver cations with the polymer chains is described through a "hopping parameter". Furthermore, given that the addition of an ionic liquid to the membrane composition promotes carrier mobility, the inclusion of a dedicated expression is necessary for a realistic description of mobile-carrier transport phenomena. The contribution of each mechanism in weighted based on the membrane composition. In order to check the model suitability, simulated values have been matched to experimental data obtained by continuous flow propane/propylene permeation experiments through PVDF-HFP/BMImBF(4)/AgBF4 composite membranes, working with 50:50 gas mixtures at different temperature and pressure. The resultant model offers good predictions for olefin flux and provides a very useful tool for process optimization and scaling-up. To our knowledge, this is the first time that mobile and fixed site carrier mechanisms performance are simultaneously modeled considering the influence of temperature, pressure and carrier loading.