An attempt was made to compare the desorption behavior of the surface oxygen complexes in an inert atmosphere with that in the O-2-gasification atmosphere. For this purpose, the transient kinetics (TK) with switching O-18(2) to O-16(2) was carried out and from this TK experiment the in situ desorption behavior of O-18(2)-containing surface complexes was evaluated during the O-16(2) gasification. The thermal stability of the O-18 complexes remaining on the carbon was analyzed by temperature-programmed desorption (TPD). In addition, the TK with switching O-2 to He was done and then the desorption behavior of the complexes was observed under He flow. It was found that the desorption behavior of the surface oxygen complexes in He is different from that in O-2. This finding indicates that the stability of the surface oxygen complexes in nongasification conditions does not correspond to the stability under O-2-gasification conditions.