CH4 decomposition (CH4 -> C + 2H(2)) on supported Co and Ni catalysts has been studied using a fixed-bed, oscillating microbalance reactor and a 5% CH4 in He feed reacted at 773 K and 101 kPa. After 45 min reaction the catalysts were regenerated by reaction of the deposited carbon with O-2 or CO2 at 773 K and 101 kPa. The effect of repeated CH4 decomposition-carbon oxidation cycles is reported. At the chosen conditions, Ni was more active and more stable than Co during the CH4 decomposition step. Although > 90% of the carbon deposited on both Co and Ni was removed by reaction with O-2, an oxidation of the active metal also occurred. In subsequent CH4 decomposition steps, an induction period was necessary to re-reduce the Co. Furthermore, the oxidized metal reacted with CH4 producing CO and CO2 as an impurity Removal of the carbon deposit by reaction with CO2 rather than O-2 significantly decreased the in the H-2. CO contamination of the produced H-2 on the Ni catalyst, However, the carbon removal rate was 20x's slower with CO2 compared to O-2. Several CH4 decomposition-carbon oxidation cycles were completed on the Ni catalyst without a significant loss in activity, whereas the Co catalyst deactivated. (c) 2008 Elsevier B.V. All rights reserved.