Kinetic behaviour of three samples of samarium oxide (cubic (Sm-1 ), monoclinic (Sm-3) and mixed cubic-monoclinic (Sm 2) ) were studied in the oxidative coupling of methane using a gradientless flow circulation system. The specific rate of C2- product formation differed by a factor of 6-8 for Sm-1 and Sm-3. The specific activity for CO formation did not depend upon the crystal structure of samarium oxide while the rate of formation of CO2 was different for the samples studied. It is proposed that formation of CO and CO2 occurs via different reaction routes. The rate of CO2 formation at high CHJO2 ratio is limited by oxidant activation or surface CO2-complex decomposition.