In recent years, gas separation has become an important step in many production process streams and part of final products. Through the use of melt co-extrusion and subsequent orientation methods, gas separation membranes were produced entirely without the use of solvents, upon which current methods are highly dependent. Symmetric three layer membranes were produced using poly(ether-block-amide) (PEBA) copolymers, which serve as a selective material that exhibits a high CO2 permeability relative to O2. Thin layers of PEBA are supported by a polypropylene (PP) layer that is made porous through the use of two methods: (1) inorganic fillers or (2) crystal phase transformation. Two membrane systems, PEBA/(PP + CaCO3) and PEBA/β-PP, maintained a high CO2/O2 selectivity while exhibiting reduced permeability. Incorporation of an annealing step either before or after orientation improves the membrane gas flux by 50 to 100%. The improvement in gas flux was a result of either elimination of strain induced crystallinity, which increases the selective layer permeability, or improvement of the PP crystal structure, which may increase pore size in the porous support layer. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39765.