Pure gas permeability through a polystyrene-b-poly(ethylene oxide) block copolymer (SEO) membrane was measured between 20 and 80 degrees C. The membrane comprised alternating polystyrene (PS) and poly(ethylene oxide) (PEO) lamellae; the average center-to-center distance between adjacent PS lamellae was 96 nm. Among the different gases considered, carbon dioxide showed the highest permeability, with values up to 200 Barrer, followed by helium, oxygen, methane and nitrogen. Gas permeability appeared to be controlled by condensability of the gas, molecular size, and molecular interactions. The melting of poly(ethylene oxide) (PEO) domains, which occurred between 40 and 60 degrees C, caused deviation from Arrhenius behavior. A simple model that accounts for transport through a composite composed of semi-crystalline PEO lamellae and amorphous PS lamellae was developed. Model results and experimental data agreed fairly well considering the simplicity of the approach. The model can readily be used to predict pure gas permeabilities of SEO copolymers with arbitrary morphologies and crystallinity. The crystalline PEO volume fractions inferred from the permeation data are within 15% of those determined by differential scanning calorimetry. (C) 2013 Elsevier B.V. All rights reserved.