A complete kinetic study of the partial oxidation of methane has been performed in a "catalytic jet-stirred reactor". The main goal of this study was to elucidate the interactions between gas-phase reactions and surface reactions and to propose a detailed heterogeneous-homogeneous mechanism. The catalyst used in this study was lanthanum oxide (La2O3). Various kinetic parameters were considered, including the temperature, the residence time, the contact time, and the amount of catalyst. The results revealed a complex behavior. In this first part of the study, the experimental results are given and discussed.