The stability of ultra-lean H-2/CO mixtures in a porous media burner is numerically investigated. The one-dimensional model considers separated energy equations for the solid and gas phases and accounts for radiative heat transfer in the solid porous foam. A simplified reaction kinetics (two-step mechanism) was employed in order to perform a linear stability analysis. This results are used to investigate the stability of the steady solutions as a function of burning velocity and flame location. The present analysis includes the effects of H-2/CO volumetric ratio, inlet mixture temperature and equivalence ratio on the flame stability. From the linear stability results it can be concluded that the insertion of inert porous media for premixed combustion promotes the ultra-lean burning of H-2/CO mixtures. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.