A theoretical model has been developed for CO2/O-2 permeation through a dual-phase membrane consisting of mixed-conducting oxide ceramic (MCOC) and molten carbonate (MC) phases. Somewhat simpler theoretical CO2 permeation equation is obtained for the special case or pure CO2 permeation case, i.e., oxygen partial pressure in the feeding gases is zero or electronic transference number of the MCOC phase is zero. The results show that CO2 permeation flux is much improved by involving oxygen permeation, which is more than one order of magnitude higher than the corresponding CO2 permeation flux for a pure CO2 permeation case. The fluxes of CO2 and O-2 increase with increasing O-2 partial pressure in the feeding gases. Both the CO2 and O-2 permeation fluxes increase with increasing electronic conductivity (sigma(h center dot)) of the MCOC phase. The CO2 permeation flux increases with increasing ionic conductivity (sigma(v center dot center dot)) of the MCOC phase at a low electronic conductivity, i.e., sigma(h center dot) <= 0.1 S/cm, while decreases with an increase of sigma(v center dot center dot) at a high electronic conductivity, i.e., sigma(h center dot) > 1 S/cm. For pure CO2 permeation, the CO2 permeation flux increases with the increase of sigma(v center dot center dot) and decreases with increasing molten carbonate volume fraction. An ordered ceramic pore structure benefits CO2 and O-2 permeation. The modeling results are compared with experimental data, and a reasonable agreement is obtained between modeling and experimental data. (C) 2009 Elsevier B.V. All rights reserved.