Ce0.9Gd0.1O2-x (CGO) was found to have useful methane steam reforming activity at solid oxide fuel cell (SOFC) operating temperatures producing H-2, CO and some CO2. The turnover frequency for steam reforming at 900 degreesC and activation energy (153 +/- 10 kJ mol(-1)) are approximately equal to those for reaction between CGO and dry methane. This is consistent with a reaction mechanism controlled by the slow reaction of methane with oxygen in CGO and a facile reaction between steam and CGO to replenish the oxygen. The addition of hydrogen to the inlet stream inhibited the reforming rate. CGO was found to be extremely resistant to carbon deposition in steam reforming conditions. (C) 2003 Elsevier B.V. All rights reserved.