The combustion characteristics of oxygen-enriched air–methane (i.e., O2/N2/CH4) flames in a premixed mode are investigated using both experimentally and numerically under atmospheric conditions for emissions reduction purposes. The investigation is carried out using a gas turbine model combustor equipped with a multihole burner that mimics gas turbine micromixer burners. The resulting flame is of jet type, and the velocity of the jet is kept at 5.2 m/s for all the considered flames. Models used in the numerical study include large eddy simulation, discrete ordinate, and partially premixed combustion for turbulence, radiation, and species models, respectively. The numerical results are validated, and a suitable agreement is achieved with experimental data. The results indicated that the temperature distribution, shape, and size of O2/N2/CH4 flames are predominantly controlled by adiabatic flame temperature (Tad). However, the oxygen fraction, rather than Tad, is responsible for the reaction progress. The emission of NO, CO, and CO2 increases with an increase in oxygen fraction, and the product formation in O2/N2/CH4 flames is less compared to their oxy-fuel (i.e., O2/CO2/CH4) counterparts, because N2 is mostly inert, compared to CO2. The latter participates significantly in flame reactions, which increases the rate of product formation in O2/CO2/CH4 flames.