Dry and steam reforming of methane is studied over Co-hexaaluminate as a prospective coking-resistant transition-metal catalyst. Kinetic measurements and X-ray diffraction investigations reveal that the formation of metallic Co and the activity of the catalyst are strongly affected by the gas composition. While co-feeding of H₂ proves to be beneficial to the conversion of methane, decreasing the ratio of CH₄ to the oxidant in the feed gas is found to be detrimental to the activity of the catalyst. A considerable inhibition effect is demonstrated particularly in the presence of H₂O. As the local gas composition inside the reactor varies with conversion, axial changes in the degree of Co reduction are observed. A microkinetic model is proposed, which accounts for the varying fractions of oxidic and metallic Co by means of oxygen surface coverages, to perform steady-state reactor simulations. Strengths and weaknesses of the approach are critically evaluated by comparing experimental and simulation results.