The effects of adding a co-metal, Pt or Rh, to Pd/-gamma-Al2O3 catalysts were studied with respect to the catalytic activity for methane combustion and compared to a Pd/gamma-Al2O3 catalyst, using both a pressurized pilot-scale and a lab-scale annular reactor. Temperature programmed oxidation (TPO) experiments were also carried out to investigate the oxygen release/uptake of the catalyst materials. Palladium showed an unstable behavior both in the pilot and lab-scale experiments at temperatures well below the PdO to Pd transformation. An addition of Pt to Pd stabilized, and in some cases increased, the catalytic activity for methane combustion.The TPO experiments showed that the oxygen release peak was shifted to lower temperatures even for low additions of Pt, i.e. Pd:Pt = 2:1. For additions of rhodium only small beneficial effects were seen. The steady-state behavior of the lab-scale annular reactor correspond well to the pressurized pilot-scale tests. (C) 2003 Elsevier B.V. All rights reserved.