Behaviors of oxygen species in the LSM/YSZ/LaAlO SOFC type reactor were investigated. The fuel cell type temperature-programmed desorption (FC-TPD) measurements were employed in three operating modes; i.e. (1) open circuit, (2) closed circuit without applied potential and (3) closed circuit with applied potential modes. Various pretreatment conditions, i.e. (a) open circuit, (b) closed circuit without applied potential and (c) closed circuit with applied potential, were investigated. The FC-TPD technique enables to discuss the oxygen species responsible for a combustion reaction and those for a coupling reaction, separately. The open circuit type FC-TPD showed that the applied potential during the pretreatment caused the increase in the amount of surface oxygen and the decrease in activation energy of desorption of oxygen at the anode catalyst. The closed circuit FC-TPD provided the combined effects of desorption and permeation. In addition, the FC-TPD analysis could correlate the behavior of adsorbed oxygen species to the NEMCA effect observed in the oxidative coupling of methane in the SOFC reactor. (C) 2003 Elsevier B.V All rights reserved.