A new membrane material having two kinds of CO2 carriers was obtained. Composite membranes were prepared with the material and support membranes. The facilitated transport of CO2 through these membranes was performed with pure CH4 and CO2 as well as CH4/CO2 mixtures containing 50 vol % CO2. The results show that the membranes possess better CO2 permeance than that of other fixed carrier membranes reported in the literature. In the measurements with pure gases, at 26degreesC, 0.013 atm of CO2 pressure, the membrane with polysulfone support displays a CO2 permeance of 7.93 x 10(-4) cm(3)/cm(2) s cmHg and CO2/CH4 ideal selectivity of 212.1. In the measurements with mixed gases, at 26degreesC, 0.016 atm of CO2 partial pressure, the membrane displays a CO2 permeance of 1.69 X 10(-4) cm(3) /cm(2) s cmHg and CO2/CH4 selectivity of 48.1.