The kinetic behavior of Ni/SiO₂ in CO methanation has been studied in a differential reactor as potassium is added to the catalyst up to 5 wt%. The potassium addition gives stronger carbon monoxide adsorption and weaker hydrogen adsorption on the catalyst, and also reduces its methanation activity. There is a maximum methanation rate for a wide range of carbon monoxide pressure and the reaction rate increases with hydrogen pressure. Potassium addition decreases CO pressure that gives the maximum methanation rate, increases slightly the order to hydrogen pressure, and increases the activation energy of methanation.