Because of the high process temperature and the high temperature to which the combustion air is preheated, NOx emissions from glass melting furnaces are extremely high. Even at these high temperatures, NOx emissions could be reduced drastically by using advanced combustion techniques such as staged combustion or flameless oxidation, as experimental work has shown. In the case of oxy-fuel combustion, the NOx emissions are also very high if conventional burners are used. Staged combustion achieves similar NOx reductions.