Partial oxidation reforming of methane using a ceramic mixed ionic (oxygen)/electronic conducting dense ceramic membrane within a solid oxide fuel cell (SOFC) stack is potentially attractive as it allows direct operation on methane. We have analysed this process using a simple model of a counter-flow fuel system in which steam and carbon dioxide from the anode channel of the SOFC provide oxygen which passes through the mixed conducting membrane to partially oxidise methane on the other side of the membrane. The model shows that the concept is feasible and that the efficiency is the same as direct methane operation. The model also gives target values for the properties of the membrane. Tracer oxygen diffusion and exchange have been measured in the family of oxides La1-xSrxFe0.8Cr0.2O3-delta under reducing conditions. The data show that these materials have the mass transport characteristics and stability required for this concept. (C) 2003 Elsevier B.V. All rights reserved.