The structure of a premixed stoichiometric flame of syngas (H2/CO/O2/Ar = 0.0667/0.0667/0.0667/0.8) stabilized on a flat burner at a pressure of 5 atm was studied experimentally and by numerical simulation. The mole fraction profiles of the reactants (H2, CO, and O2) and the major (H2O and CO2) and intermediate (O, OH, HO2, and H2O2) combustion products were measured by molecular beam mass spectrometry. The experimental data were compared with those calculated using three detailed chemical-kinetic mechanisms proposed in the literature for oxidation of a H2/CO mixture. Good agreement was found between the results of the experiment and simulation. Calculations of the structure of the flame of the same composition at a pressure of 1 and 10 atm were performed to establish the effect of the pressure on the chemical reaction kinetics in the syngas flame. The results were explained by kinetic analysis of the mechanisms.