The power-to-gas process for the chemical storage of renewable energy in methane as a storage molecule requires a carbon source, for which industrial exhaust gases are very promising because of their availability in large quantities. The composition of these gas streams, however, is often characterized by a mixture of CO and CO2. Because of the rather complex reaction mechanism, though, the methanation of CO/CO2 mixtures using nickel catalysts is not yet fully understood, and appropriate reaction kinetics required for the reactor design are still lacking. Therefore, we report the experimental results on the methanation of various mixtures of CO and CO2. The data are further evaluated by a model-based approach in order to derive reaction kinetics capable for the reactor design in a typical range of operating conditions. The results also reveal two kinetic regimes depending on the fraction of CO in the CO/CO2 mixture, which is accounted for in the proposed kinetics.