The reburning process with natural gas is an effective technique which can be applied in existing coal combustors in order to reduce the NOx emissions. The importance of the burnout zone in this process is great, because significant amounts of CO, unburned fuel and reactive nitrogen can reach this zone. The influence of the temperature and the air excess introduced in the burnout zone on the concentration of the nitrogenous species has been studied. Experimental results have been determined of the concentrations of NO, HCN and NH3 in the exit gas for temperatures ranging between 900 and 1100 degrees C and air excesses between 5 and 15%. An empirical correlation which fits the output NO concentration has been obtained. A simplified model has been developed to predict the output concentrations of the most interesting nitrogenous species.