A numerical and experimental investigation of a burner operating in MILD combustion regime and fed with methane and methane-hydrogen mixtures (with hydrogen content up to 20% by wt.) is presented. Numerical simulations are performed with two different combustion models, i.e. the ED/FR and EDC models, and three kinetic mechanisms, i.e. global, DRM-19 and GRI-3.0. Moreover, the influence of molecular diffusion on the predictions is assessed. Results evidence the need of a detailed chemistry approach, especially with H(2) to capture the volumetric features of MILD combustion The inclusion of molecular diffusion influences the prediction of H(2) distribution; however, the effects on the temperature field and on the major species are negligible for the present MILD combustion system. A simple NO formation mechanism based on the thermal and prompt routes is found to provide No emissions in relatively good agreement with experimental observations only when applied on temperature fields obtained with the EDC model and detailed chemistry. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.