A process and apparatus for separating a feed containing hydrogen, carbon monoxide, methane, and optionally nitrogen to form a product gas having a desired H2:CO molar ratio and optionally a hydrogen product gas and a carbon monoxide product gas. The feed is partially condensed to form a hydrogen-enriched vapor fraction and a carbon monoxide-enriched liquid fraction. The hydrogen-enriched vapor fraction and carbon monoxide-enriched liquid fraction are combined in a regulated manner to form an admixture, which is cryogenically separated to form the product mixture having the desired H2:CO molar ratio.