In this research, the integrally asymmetric polyethersulfone membrane were prepared using phase inversion technique.As an interesting result, the membrane exhibits rubbery PDMS behavior for H2S containing feeds and displays a glassy PES membrane for CO2/CH4 mixed gas. The effects of sodium dodecyl sulphate (SDS), cetyle three methyl ammonium bromide (CTAB), and Triton X-100 on structure and performance of polyethersulfone membranes for carbon dioxide separation from methane were investigated. The results indicate that addition of surfactants in the casting solution increases the membrane porosity and membrane gas permeance and decreases CO2/CH4 ideal selectivity, except for Triton X-100 which increases CO2/CH4 selectivity. Asymmetric gas separation membranes of polyethersulfone (PES) andpolyethersulfone/polyurethane (PU) were prepared with different blend compositions.