The kinetics of the steam reforming of methane over a coprecipitated Ni/Al₂O₃ catalyst have been examined in the temperature range 773 to 953 K and in the pressure range 0–10 Torr. Examination of the stoichiometry of the reaction showed that a catalyst freshly reduced in hydrogen at 873 K was further reduced by the reaction mixture. This is taken to imply that reduction of some phase such as NiAl₂O₄ was occurring. The rate determining step of the reaction on the fully reduced catalyst under reducing conditions was found to be the rate of adsorption of methane and competition for the adsorption sites by water occurred. The water–gas shift reaction did not proceed appreciably, and this implies that significant CO and CO₂ adsorption does not occur on the catalyst surface; this is in agreement with the kinetic results. Experiments involving D₂O or D₂ helped to confirm these conclusions.