Hydrogen is produced by reacting carbon monoxide with steam at a temperature of at least 200.degree.F. in the presence of a supported catalyst containing: (1) at least one alkali metal compound derived from an acid having an ionization constant below 1 .times. 10.sup..sup.-3, (2) a metallic hydrogenation-dehydrogenation material, and (3) a halogen moiety. The ratio of metal component to alkali metal compound, each calculated on the basis of the oxide thereof, ranges from 0.0001 to about 10 parts by weight per part by weight of the alkali metal compound. The halide constituent is present in amounts in excess of about 0.01 weight %, based on total catalyst. A preferred catalyst composition comprises potassium carbonate, a mixture of cobalt and molybdenum oxides and combined chlorine contained on an alumina support.