Measurements have been made on the separation of CO2 from gas phase by aqueous absorbents (water and diethanolamine solution) using non-porous and microporous hollow fibre membrane modules. The use of an absorbent liquid in the permeate side of the permeator enhances CO2 separation and reduces the requirements for a high pressure ratio across the membrane. A mathematical model based on the effective permeability of the gaseous mixtures has been used to assess the performance of both hollow fibre membranes, and a correlation for the shell side mass transfer has been developed. Overall mass transfer in the microporous and non-porous membranes is dominated by the liquid film coefficient and a combination of liquid film and membrane resistances, respectively.