The chemistry of nitrogen species and the formation of NOx in hydrogen combustion are analyzed here on the basis of a large set of experimental measurements. The detailed kinetic scheme of H-2/O-2 combustion was updated and upgraded using new kinetic and thermodynamic measurements, and was validated over a wide range of temperatures, pressures and equivalence ratios. The mechanism's performance at high pressures was greatly improved in particular by adopting higher rate parameters for the H + OH + M = H2O reaction. The NOx sub-mechanism was further validated and updated. The kinetic parameters of the NO2 + H-2 = HONO + H and N2H2 + NO = N2O + NH2 reactions were updated in order to improve model predictions in specific conditions. Sensitivity analyses were carried out to determine which reactions dominate the H-2/O-2 and H-2/NOx systems at particular operating conditions. Good overall agreement was observed between the model and the wide range of experiments simulated. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All fights reserved.