Fuel nitrogen release and its conversion to nitrogen oxides in pressurized fluidized bed combustion have been recently studied in a laboratory-scale batch reactor, which can be controlled at well-defined operating conditions, The conversion to nitrogen oxides during devolatilization and char oxidation was investigated under the base operating conditions (T-b = 850 degrees C, p = 11 bar, O-2 = 3% v/v, V-f = 0.24 m/s) with 10 different fuels, from high-volatile peat to relatively low-volatile coke. The effects of other parameters, such as bed temperature, oxygen concentration in the fluidizing gas, pressure, fluidizing velocity, and particle size, on the fuel-N behavior were compared in detail with three of the fuels : lignite, Illinois No. 6 coal, and Kiveton Park coal. A special focus of this study was the influence of pressure which was divided into two parts : oxygen partial pressure and total pressure. Results showed that fuel nitrogen conversion to NOx and N2O was dependent on fuel type and operating parameters relating strongly to the combustion behavior of fuel batch. Concerning the conversion to NOx, the influence of oxygen partial pressure by changing oxygen concentration in the inlet gas was more marked than that by changing pressure, and total pressure showed a different trend to that when the oxygen partial pressure was changed. Both homogeneous and heterogeneous reactions contributed to the formation of NOx and N2O. The observations indicated that in the batch reactor the reduction mechanism also played a significant role in the emissions of nitrogen oxides under the examined conditions.