This experimental and modeling study aimed at better understanding the impact of the operating conditions on the interplay between ammonium nitrate (AN) decomposition pathways and their coupling with gas-phase chemistry. Experimental analysis and kinetic modeling were combined to elucidate the role of operating conditions on ammonium nitrate thermal decomposition. A new condensed-phase semi-detailed kinetic mechanism was developed and validated against original experiments performed in this study and experiments from other groups. This mechanism was coupled to a gas-phase mechanism, making it possible to quantify the contributions of condensed-phase and gas-phase reaction pathways to AN thermal decomposition at different heating rates. The study revealed that T-50 (temperature at 50% conversion) increases strongly with the heating rate, favoring highly activated reactions. Even at typical burning surface temperatures (350 degrees C), gas-phase reactions involving nitramide and nitric acid play a significant role. The thermal deNOx pathway and hydroxylamine decomposition impact significantly NH3 consumption in the monopropellant flame zone. (C) 2014 Elsevier B.V. All rights reserved.