A process for producing a carbon monoxide-containing product from a feed containing hydrogen, carbon monoxide, methane, nitrogen and optionally argon, the process comprising: partially condensing the feed to provide a first hydrogen-enriched vapor fraction and a first hydrogen-depleted liquid fraction; stripping hydrogen from the first hydrogen-depleted liquid fraction in a first fractionator to form a second hydrogen-enriched vapor fraction and a hydrogen-freed liquid fraction; separating at least a portion of the hydrogen-freed liquid fraction in a second fractionator to form a nitrogen-enriched vapor fraction and a nitrogen-depleted liquid fraction containing carbon monoxide and methane; separating an at least partially vaporized feed containing carbon monoxide and methane in a third fractionator to form the carbon monoxide-containing product and a methane-enriched liquid fraction; characterised in that: cooling a portion or all of the nitrogen-enriched vapor fraction by indirect heat exchange with a portion of the nitrogen-depleted liquid fraction and by indirect heat exchange with a portion or all of the methane-enriched liquid fraction to form a condensate from the portion or all of the nitrogen-enriched vapor fraction, and to form the at least partially vaporized feed from the portion of the nitrogen-depleted liquid fraction, and to form a vapor boil-up and a methane-containing bottoms product from the portion or all of the methane-enriched liquid fraction; introducing at least a portion of the vapor boil-up to the third fractionator to provide stripping vapor; and introducing at least a portion of the condensate to the second fractionator as reflux. partially condensing the feed to provide a first hydrogen-enriched vapor fraction and a first hydrogen-depleted liquid fraction; stripping hydrogen from the first hydrogen-depleted liquid fraction in a first fractionator to form a second hydrogen-enriched vapor fraction and a hydrogen-freed liquid fraction; separating at least a portion of the hydrogen-freed liquid fraction in a second fractionator to form a nitrogen-enriched vapor fraction and a nitrogen-depleted liquid fraction containing carbon monoxide and methane; separating an at least partially vaporized feed containing carbon monoxide and methane in a third fractionator to form the carbon monoxide-containing product and a methane-enriched liquid fraction; characterised in that: cooling a portion or all of the nitrogen-enriched vapor fraction by indirect heat exchange with a portion of the nitrogen-depleted liquid fraction and by indirect heat exchange with a portion or all of the methane-enriched liquid fraction to form a condensate from the portion or all of the nitrogen-enriched vapor fraction, and to form the at least partially vaporized feed from the portion of the nitrogen-depleted liquid fraction, and to form a vapor boil-up and a methane-containing bottoms product from the portion or all of the methane-enriched liquid fraction; introducing at least a portion of the vapor boil-up to the third fractionator to provide stripping vapor; and introducing at least a portion of the condensate to the second fractionator as reflux. cooling a portion or all of the nitrogen-enriched vapor fraction by indirect heat exchange with a portion of the nitrogen-depleted liquid fraction and by indirect heat exchange with a portion or all of the methane-enriched liquid fraction to form a condensate from the portion or all of the nitrogen-enriched vapor fraction, and to form the at least partially vaporized feed from the portion of the nitrogen-depleted liquid fraction, and to form a vapor boil-up and a methane-containing bottoms product from the portion or all of the methane-enriched liquid fraction; introducing at least a portion of the vapor boil-up to the third fractionator to provide stripping vapor; and introducing at least a portion of the condensate to the second fractionator as reflux.