Catalytic partial oxidation (CPO) reactors have complex concentration and temperature gradients which make it difficult to understand the mechanism of autothermal operation. Previous research in the Schmidt group on methane CPO using the capillary sampling technique has shown the existence of two zones - oxidation and reforming [1-4]. Nearly (>90%) all of the oxygen in the feed is converted within the first 2 mm of the catalyst bed. In this paper, temperature and concentration profiles during the CPO of methane and dimethyl ether CH3OCH3, an oxygenated hydrocarbon, are presented. Results with the two feeds are compared and the nature of the profiles was similar, with sharp gradients existing in the oxidation zone with slower chemistries in the reforming section. The rhodium catalyst in the oxidation zone during methane CPO was also analyzed using XPS and XRD and shown to be rhodium metal. (C) 2014 Elsevier B.V. All rights reserved.