The objective of the present study was to experimentally investigate and compare the characteristics of three oxygen-enhanced combustion (OEC) methods; premix enrichment (PE), air-oxy/fuel combustion (AO), and additionally also oxygen lancing (OL) method. The overall oxygen concentration varied from 21% to 38%. Combustion tests were carried out using the gas burner with the thermal input of 750 kW fired by natural gas. The characteristics of OEC methods, such as the concentration of nitrogen oxides and carbon monoxide in flue gas, in-flame temperatures distribution in the horizontal symmetry plane of the combustion chamber, heat flux to the combustion chamber wall, flue gas temperature, and the stability of flame were investigated. NOx emissions increased by more than 40 times and by 20 times for the PE method. The tests using the AO and OL methods with NOx emissions below 150 mg/Nm3 at all oxygen concentrations showed significantly better results. For all OEC methods, radiative heat transfer increased with increasing oxygen concentration. The available heat was 20% higher at 38% O2 than at 21% O2. The flue gas temperature decreased with increasing oxygen concentration, which was affected by a decrease in N2 concentration in the oxidizer and a simultaneous increase in radiant heat flux.