An emerging membrane morphology with future potential is mixed matrix membranes composed of two interpenetrating matrices of different materials. In this study, mixed matrix membranes of an amorphous glassy polymer(polyethersulfone) and hydrophilic zeolite (4A) were prepared. An elaborate membrane preparation technique that enables incorporation of high zeolite loading into the membrane was developed. Performance of membranes was tested by using a laboratory-scale gas separation apparatus. The permeation rates of N-2, CH4, Ar, O-2, CO2, and H-2 were evaluated through a dense homogeneous PES membrane and a PES-4A mixed matrix membrane. For the mixed matrix membrane, gas permeabilities were either not changed or significantly improved. The ideal separation factors of economically important gas pairs were substantially increased due to the faster permeation of H-2 and CO2 through the mixed matrix membrane. In order to understand their interaction with each ether and with membrane matrices, permeabilities and selectivities of CO2/CH4, CO2/Ar, and H-2/CH4 binaries as a function of gas composition were measured through a dense homogeneous PES membrane and a PES-4A mixed matrix membrane. Observed selectivity independence with respect to gas composition for a dense homogeneous PES membrane indicates that ternary interactions and factors like plasticization and gas fugacity do not affect the gas permeation mechanism appreciably for this type of membrane. However, selectivities demonstrated a strong concentration dependency through a PES-4A mixed matrix membrane. For CO2/CH4 and CO2/Ar systems, when the CO2 concentration in the feed increased, selectivity decreased linearly. In the case of H-2/CH4 binaries, unlike the cases with CO2 binaries, a higher H-2 concentration in the feed caused higher selectivity values, The trend was also linear with H-2 concentration in the feed. This indicates that. for mixed matrix membranes, the existence of a third component causes the gas molecules to interact with the heterogeneous membrane matrix, affecting selectivities. Selectivity dependency indicates the importance of gas-membrane matrix and gas-gas-membrane matrix interactions.