Selective gas barriers are of prime importance in thin polymer membranes. The focus of this work was to find a polymer membrane that allows the transport of H-2 and acts as a barrier to CO2 and chlorinated organics. Membrane screening has included the following testing: single gas permeability measurements, mixed gas separations, and polymer physical characterization. Single gas permeability measurements were made using the time-lag method for five gases (H-2, O-2, N-2, CO2, and CH4). Permeability coefficients and selectivities for the gas pair H-2/CO2 are presented. Mixed gas separations were performed to measure actual separation factors for H-2/CCl4 and to determine the effects on hydrogen permeability caused by exposing polymers to chlorinated hydrocarbons. The results of basic polymer characterization, such as polymer density and glass transitions, are addressed.