The CO hydrogenation activity of a Ru/Fe/TiO2 catalyst with reactant gases containing H2O was investigated for application in the production of substitute natural gas containing CH4 as the major component and C-2-C-4 hydrocarbons as the minor components. The total higher heating value (HHV) of the C-1-C-4 hydrocarbon products in the complete CO conversion was higher than 45 MJ/m(3)(Normal) for the CO hydrogenation using reactant gases containing H2O. Moreover, the HHV of the C-1-C-4 hydrocarbon products in the complete CO conversion was higher than 45 MJ/m(3)(N) over a wider temperature range when the H-2/CO molar ratio in the reactant gas was 2.5 rather than when it was 3.0.