The primary methods of reduction are presently among the cheapest methods of reducing gaseous pollutants and, through the appropriate preparation of solid fuels, also dusty pollutants. A primary nitrogen oxide reduction method that is most frequently used in the Polish conditions is the gradation of air; however, more and more attention has also been focused recently on another primary reduction method, namely the gradation of fuel, called also reburning. Experiments carried out on a worldwide scale indicate that the gradation of fuel, alongside the gradation of air, is one of the most efficient primary nitrogen reduction methods, which enables the co-combustion of traditional energy fuels with waste fuels and biofuels. The effect of the type of reburning fuel on the efficiency of nitrogen oxide emission reduction were examined within the present work. Both traditional fuels, such as natural gas and fuel oil, as well as biomass of plant origin in its three states of aggregation, were subjected of analysis. The obtained results have shown that the type of reburning fuel has a substantial influence on both NO, emission and the efficiency of nitrogen oxide emission reduction.