Flameless combustion in a laboratorial combustor is numerically simulated. A comparison of different turbulence and combustion models and different chemical reaction mechanisms is reported. The results are validated using experimental data obtained in a small-scale combustor fired with methane. The calculations show that the different turbulence models employed do not yield significant differences, as far as the mean temperature and major species are concerned. Combustion models based on the flamelet concept predict a steep rise in temperature and CO2 molar fraction along the combustor axis in comparison with the experimental data, even though they yield satisfactory predictions elsewhere. In contrast, the eddy dissipation concept along with a detailed reaction mechanism yields rather good predictions, particularly if the most detailed reaction mechanism is employed. The N2O mechanism is responsible for most of the predicted NO molar fraction, which is of the order of 10ppm, clearly exceeding the experimental data.