We used molecular simulations to assess the performance of zeolite imidazolate framework (ZIF) based mixed matrix membranes (MMMs) for CO2/CH4, H-2/CH4, and H-2/CO2 separations. The gas permeability of ZIF based MMMs was estimated based on the gas permeability of pure ZIFs obtained from molecular simulations and the gas permeability of pure polymers obtained from experimental studies. Predicted gas selectivity and permeability were compared with the available experimental data of MMMs in which ZIF-8 and ZIF-90 were used as filler particles. After showing the good agreement between the predictions of theoretical methods and experiments, we estimated gas selectivity and permeability of 360 new MMMs composed of 15 different ZIFs and 24 different polymers. Our results showed that ZIF-11 based MMMs exhibit high performance for separation of CO2/CH4 whereas ZIF-65 based MMMs are good candidates for H-2/CO2 separation.