The effect of K promotion on the CO hydrogenation activity and C2−C4 hydrocarbons selectivity of the 15 wt % Ni−10 wt % Mo/Al2O3 catalyst was investigated in the 498−548 K range using unpromoted and 1−3 wt % K-promoted samples. CO2 methanation tests at 523 K were used as a probe to confirm activity trends. Intrinsic kinetic data were obtained in the initial rate region on both unpromoted and 1 wt % K-promoted Ni−Mo catalysts. K promotion of the bimetallic Ni−Mo catalyst decreases both the activity and the specific activity of the Ni sites while increasing the C2−C3 olefin-to-paraffin ratio. The surface carbide mechanism with dissociative adsorption of hydrogen as the rate-limiting step gives the most plausible kinetic model among the models tested for both Ni−Mo and Ni−Mo−K catalysts.