A folded-plate reactor for the selective CO oxidation in the H-2-rich feed of a PEM fuel cell has been designed, manufactured and experimentally tested. The novel, liquid-cooled compact reactor with distributed air-side feeds meets its goals in reducing the CO content in the reformate from 1% to around 50 ppm for a total flow corresponding to a load of 1.5 kW(th). (c) 2007 Elsevier Ltd. All rights reserved.