The heat flows associated with conversion of n-hexane [GRAPHIC] on H-ZSM-5 and H(Zn)-ZSM-5 were measured for reaction at 60 bar and both 673 and 773 K for application to endothermic reforming for hypersonic flight. The heat flows were determined by measuring the power required to maintain a constant reactor temperature upon introduction of flowing n-hexane. The acid-catalyzed reactions over H-ZSM-5 were found to be only mildly endothermic(<10 kJ/mol) at low conversions and exothermic at all conversions above 50%. The reactions on H(Zn)-ZSM-5 were significantly more endothermic (40-50 kJ/mol) for conversions of <70%; however, the reactions also became exothermic at very high conversions. Measurements of the product distributions showed that the reaction endothermicity for H(Zn)-ZSM-5 at-lower conversions was likely due to the formation of significant amounts of benzene, toluene, and xylene, but that these were converted to higher-molecular-weight products at high conversions. Implications of these results for preparing improved endothermic-reforming catalysts is discussed.