A better knowledge of the combustion chemistry in very lean flames is required to improve flame stability and control the presence of oxygenated species as final products. In this work, the chemical structure of lean premixed propane-oxygen-nitrogen flames stabilized on a flat flame burner at atmospheric pressure was determined experimentally. The species mole fraction profiles were also computed by the Premix code (Chemkin 11 version) and three recently proposed mechanisms. Globally, the agreement between measured and computed mole fractions profiles is similar, despite large differences in the number of reactions in each mechanism. Pathways analyses show that only weak variations are observed in the relative importance of the main oxidation routes when the equivalence ratio is decreased from 0.9 to 0.5. (c) 2005 The Combustion Institute. Published by Elsevier Inc. All rights reserved.