In this work we experimentally investigate the onset of the diffusive-thermal instabilities for flat burner stabilized methane-air flames at normal pressure. The structure and dynamics of combustion fronts are studied by using visual imaging, including high-speed video recording, spectroscopic and acoustic measurements. Numerical simulations with a one-dimensional model for a burner stabilized flame with detailed reaction mechanisms are also conducted. The critical conditions for the emergence of flame oscillations and the period of pulsations are determined. The experimental data obtained with different techniques are found to be in good agreement and also correlate with the numerical results. The numerically calculated data are shown to be sensitive to the choice of the reaction mechanism. Thus a direct measurement and calculation of the critical conditions and the characteristics of flame oscillations open a new perspective for the verification and validation of detailed reaction mechanisms. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.