The catalytic partial oxidation (CPO) of CH 4 to synthesis gas over a 4 wt% Rh/ α-Al 2O 3 catalyst was investigated by means of a short contact time annular reactor, specifically designed for testing very fast and exothermic reactions. Data were collected by feeding CH 4/O 2/inert gas mixtures, at varying temperature (from 350 to 850 °C), GHSV (up to 4.5 × 10 6 N l / K g cat / h ), O 2/CH 4 ratio (from 0.56 to 1.3), reactant dilution (1 to 27% CH 4 v/v) and adding CO 2 (1%) and H 2O (1 and 2%) to the standard feed. Steam reforming, CO 2 reforming, water gas shift (WGS), reverse-WGS, H 2 and CO combustion tests were also carried out to refine the study. A quantitative analysis of the experimental data was performed by a 1D mathematical model of the reactor, wherein a molecular kinetic scheme of the process was incorporated. The scheme consists of CH 4 total oxidation and reforming, the water gas shift and reverse water gas shift reactions, and H 2 and CO post-combustion reactions. On the basis of experimental data and numerical analysis, it was found that, under the CPO conditions: (1) the kinetic role of CO 2 reforming is negligible, so that steam reforming and CH 4 total combustion alone can account for the consumption of CH 4; (2) oxidation and steam reforming of methane have comparable intrinsic kinetics under differential conditions, but surface coverages differently influence the reaction rates under integral conditions; (3) the direct and the reverse water gas shift reactions (WGS and RWGS), when far from the chemical equilibrium, have independent kinetics; (4) the process kinetics is significantly affected by the dilution of the reacting mixture: since the global reaction order is lower than 1, conversion and selectivity decrease at decreasing dilution. Part I of the work deals with the development and the validation of the proposed kinetic scheme; Part II deals with the analysis of CO 2 reforming and RWGS experiments and supports the assumption that CO 2 reforming can be excluded form the CPO kinetic scheme.