In situ time-resolved FTIR spectroscopy was used to study the reaction mechanism of partial oxidation of methane to synthesis gas and the interaction of CH4/O-2/He (2/1/45) gas mixture with adsorbed CO species over SiO2 and gamma -Al2O3 supported Rh and Ru catalysts at 500-600 degreesC. It was found that CO is the primary product for the reaction of CH4/O-2/He (2/1/45) gas mixture over Hz reduced and working state Rh/SiO2, catalyst. Direct oxidation of methane is the main pathway of synthesis gas formation over Rh/SiO2 catalyst. CO2 is the primary product for the reaction of CH4/O-2/He (2/1/45) gas mixture over Ru/gamma -Al2O3 and Ru/SiO2 catalysts. The dominant reaction pathway of CO formation over Ru/gamma -Al2O3 and Ru/SiO2 catalysts is via the reforming reactions of CH4 with CO2 and H2O. The effect of space velocity on the partial oxidation of methane over SiO2 and gamma -Al2O3 supported Rh and Ru catalysts is consistent with the above mechanisms. It is also found that consecutive oxidation of surface CO species is an important pathway of CO2 formation during the partial oxidation of methane to synthesis gas over Rh/SiO2 and Ru/gamma -Al2O3 catalysts. (C) 2000 Elsevier Science B.V. All rights reserved.