An experimental investigation is performed to establish the optimal operating conditions of a porous media after-burner integrated with a I kW solid oxide fuel cell (SOFC) system fed by a natural gas reformer. The compositions of the anode off-gas and cathode off-gas emitted by the SOFC when operating with fuel utilizations in the range 0-0.6 are predicted using commercial GCTool software. The numerical results are then used to set the compositions of the anode off-gas and cathode off-gas in a series of experiments designed to clarify the effects of the fuel utilization, cathode off-gas temperature and excess air ratio on the temperature distribution within the after-burner. The experimental results show that the optimal after-burner operation is obtained when using an anode off-gas temperature of 650 degrees C. a cathode off-gas temperature of 390 degrees C, a flame barrier temperature of 700 degrees C, an excess air ratio of 2 and a fuel utilization of U-f = 0.6. It is shown that under these conditions, the after-burner can operate in a long-term, continuous fashion without the need for either cooling air or any additional fuel other than that provided by the anode off-gas. (C) 2009 Elsevier B.V. All rights reserved.