The effect of the Pd loading in NiO-MgO solid solution was investigated in oxidative steam reforming of methane under atmospheric and pressurized conditions. The small amounts of Pd addition on Ni0.2Mg0.8O can inhibit the oxidation of Ni species and the mixture can maintain the reforming ability at low W/F conditions under atmospheric pressure, where Ni0.2Mg0.8O catalyst deactivated. In addition, Ni0.2Mg0.8O catalyst improved remarkably, gaining both high activity and excellent stability by the addition of small amounts of Pd under pressurized conditions. The deactivation rate was closely related to the amount of deposited carbon. Characterization results of TEM, TPR, EXAFS and FTIR suggest that Pd-Ni alloy particles are formed on Pd/Ni0.2Mg0.8O catalysts. The Pd-Ni alloy particles with a low ratio of I'd to Ni can play an important role in the high resistance to carbon deposition. (c) 2006 Elsevier B.V. All rights reserved.