NOVELTY - A two stage-carbon monoxide preferential oxidation article comprises an article inlet (5), an article outlet (6), an upstream chamber (2) with two upstream zones, a downstream chamber, and a mixing chamber (3). The article includes single injection chamber (1) having an oxygen gas injector (7). The oxygen gas injector is capable of directing a greater proportion of an oxygen-containing gas to the second group of channels than the first group of channels. The second group of passages is disposed in an annular pattern about the substrate's longitudinal axis.    USE - The article is used for selectively removing carbon monoxide from inlet gas stream, e.g. hydrogen stream containing carbon monoxide to form purified hydrogen stream for fuel cell.    ADVANTAGE - The article reduces carbon monoxide to the desired level, has simplified the design, reduces volumes, and reduces reactor costs.    DETAILED DESCRIPTION - A two stage-carbon monoxide preferential oxidation article comprises an article inlet, an article outlet, an upstream chamber with two upstream zones, downstream chamber, and mixing chamber. The first upstream zone comprises an upstream Prox catalyst. The second upstream zone is free of Prox catalyst. The downstream chamber comprises a downstream Prox catalyst. The downstream chamber is in fluid communication with the article outlet. The mixing chamber is between the upstream and downstream chambers. The mixing chamber is in fluid communication with the upstream and downstream chambers. The article includes single injection chamber having an oxygen gas injector. The oxygen gas injector is capable of directing a greater proportion of an oxygen-containing gas to the second group of channels than the first group of channels. The second group of passages is disposed in an annular pattern about the substrate's longitudinal axis. An INDEPENDENT CLAIM is also included for removing carbon monoxide from an inlet gas stream.    DESCRIPTION OF DRAWING(S) - The figure shows upstream chamber used in two stage carbon monoxide preferential oxidation article.    Single injection chamber (1)    Upstream chamber (2)    Mixing chamber (3)    Article inlet (5)    Article outlet (6)    Oxygen gas injector (7)