The transport performances of carbon dioxide and methane were studied in polyethersulfone, polyethersulfone/polyeterurethane (PES-ETPU) and polyethersulfone/polyestherurethane (PES-ESPU) blend membranes separately with different compositions. The variations in the structural characteristics of PES membrane after incorporation of ESPU and ETPU were investigated by different techniques. Additionally, the effect of pressure and composition on the permeance of CO2, CH4 and ideal selectivity of CO2/CH4 were checked on the membranes. The results revealed that the morphology of the blend membranes was affected by two opposite factors: thermodynamic enhancement and kinetic hindrance. The membranes with denser sponge layers were formed at lower ratio of PU/PES, while more porous structure with enlarged macrovoids membranes were observed at higher PU content. The results indicated that adding PU to PES membrane, caused permeance improvement of the gases with nearly no change and/or reduction in ideal selectivity of CO2/CH4. Moreover, PES-ETPU membranes showed higher permeability and less CO2/CH4 selectivity in comparison with PES-ESPU samples. For PES-ESPU membrane containing 1.5% ESPU, CO2 permeance at 10 bar was improved up to 20% with almost no change in CO2 /CH4 selectivity with respect to PES. Finally, response surface methodology was used to evaluate the effects of the operating parameters on the permeance and ideal selectivity. (C) 2017 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.