For the purposes of optimising important system parameters in direct internally reforming (DIR) solid oxide fuel cell (SOFC) systems, a detailed knowledge of the methane steam reforming rate on the anode is needed. In order to shed light on the present poorly understood kinetics, a study of the methane steam reforming rate given by a typical thin electrolyte-supported nickel/zirconia SOFC anode has been carried out using a tubular plug flow differential reactor. These tests were essentially gradientless. The reaction rate was studied as a function of temperature (700-1000 degrees C) and the partial pressure of methane (2-40 kPa), hydrogen (10-70 kPa) and steam (10-70 kPa). The total pressure was nominally 1 arm. The reaction was first order in methane with a weak positive effect of hydrogen, and a stronger negative effect of steam, The kinetics were complicated by the fact that reaction orders in hydrogen and steam were either temperature dependent and/or depended on the partial pressures of other components in the gas mixture. Furthermore, Arrhenius-type plots gave gradients which were dependent on the steam partial pressure. It is clear from this study that the reaction cannot be represented as simply as is generally attempted in the literature. An improved rate equation has been derived.