A series of world-traded coal samples has been tested using the Imperial College high temperature wire mesh apparatus (HTWM) in order to assess the relationship between high temperature (1600 degrees C) char nitrogen content and NOx formation in Hemweg Power Station (in the Netherlands) using deep furnace air staging. A linear relationship between high temperature char nitrogen and NOx formation has been confirmed. These results suggest that high temperature char N content is the main factor limiting NOx emissions with deep air-staged combustion. Char N and (hence apparently deep air-staged NOx) can be predicted with an accuracy of approximately +/- 20% for most coals from the coal proximate and ultimate analysis-but this might not be sufficient for stations operating close to their emission limits. Measuring high temperature char N directly reduces the likely uncertainty in deep air-staged NO, emissions for coals (and most blends) to approximately +/- 10%. Its use should be considered on a routine basis for coal selection on plants employing this technology. (c) 2005 Elsevier Ltd. All rights reserved.