Differential Thermal Analysis (DTA) and Differential Barometric Analysis (DBA) were used to study the combustion of aqueous urea ammonium nitrate alternative fuel, a low carbon nitrogen-based hydrogen storage medium, under varied pressures (up to 27 MPa) in a constant volume analyzer. The thermal processes governing the fuel combustion under applied pressure were investigated at elevated temperatures (up to 500 degrees C). Three distinct exothermic effects were observed during reaction, and all three shifted towards higher temperatures with increased pressure. A change in combustion mechanism was suggested to occur at 5 MPa, and the calculated activation energy of the low pressure region (P < 5 MPa) was 209 kJ mol (1), in agreement with the literature value for radical ammonium nitrate decomposition. Deduction of the reaction pathway is crucial for a basic understanding of the fuel's combustion mechanism. (C) 2015 Elsevier Ltd. All rights reserved.