A series of experiments on the facilitated transport of CO2 through supported liquid membranes containing monoethanolamine (MEA) and diethanolamine (DEA) was performed. The feed gas was a mixture of CO2 and CH4, and the CO2 partial pressure pCO2,F was in the range from 0.05 to 0.97 atm. Compared to the MEA membranes, the DEA membranes showed a little higher permeation rate of CO2 since the equilibrium constant of the reaction between CO2 and MEA is too large for CO2 to be released to the receiving phase rapidly. When pCO2,F and the MEA concentration were 0.05 atm and 4 mol/dm3, respectively, the separation factor α(CO2/CH4) was about 2000. It was found that if the membrane thickness multiplied by the square root of the tortuosity factor of the microporous support membrane is used as the effective pore length, the experimentally observed permeation rates of CO2 can be satisfactorily simulated by the theory of facilitated transport of CO2 through aqueous amine membranes. A method for estimating the solubili...