NO and NO2 formation in PF oxy-fuel firing was investigated for a high volatile bituminous coal and a high-sulfur lignite coal. Results obtained under various oxy-fuel atmospheres were compared with those produced during air combustion. Experiments involving NO injection under dry and under wet conditions were also conducted in order to simulate dry and wet flue gas recycles respectively. NO emissions were observed to be significantly lower during all oxy-fuel cases for both the high volatile bituminous coal and the lignite coal in comparison to air combustion. Overall trend was an increase in NO emissions with increasing inlet oxygen concentration for the oxy-fuel cases. The presence of steam (wet flue gas recycle) decreases NO formation from fuel nitrogen as well as reduces recycled NO. The efficiency of steam in recycled NO reduction wanes however with increasing inlet oxygen concentration. NO2 formation in oxy-fuel environment increases as a result of increasing oxygen partial pressure but these increases are not substantial. Steam addition to the oxy-fuel oxidant gases yields substantial increases in NO2/NOX ratios for high volatile bituminous coal in all cases while for lignite coal, the ratio remained low. (c) 2013 Elsevier Ltd. All rights reserved.