Abstract: A process for producing hydrogen gas by reacting steam with a gas mixture containing carbon monoxide, carbon dioxide and hydrogen to produce a hydrogen-enriched product gas and subjecting the product gas to pressure swing adsorption to produce a high purity hydrogen product and a hydrogen-depleted waste gas is improved by drying, where necessary, part of the gas mixture and subjecting the dry gas mixture to pressure swing adsorption using a carbon monoxide-selective adsorbent to produce a high purity carbon monoxide product gas and a carbon monoxide-depleted waste gas. Where the gas mixture is produced by endothermic reaction, one or both of the hydrogen-depleted waste gas and the carbon monoxide-depleted waste gas can be used as fuel to supply heat for the endothermic reaction.