An onboard autothermal reformer (AIR) integrated with a SOFC stack offers potential for high energy efficiency and utilization, low emission and quiet operation avoiding cost associated with hydrogen storage and infrastructure. Such a system can be a viable and attractive option especially for military's need for quiet and less pollutant Auxiliary Power Unit (APU) and Mobile Electric Power (MEP) units in temporary and permanent base camps [1,2]. A 5 kW(e) Solid Oxide Fuel Cell (SOFC) system operating on desulfurized JP-8 fuel was modeled using Aspen Plus process simulation software to examine the effects of oxygen to carbon ratio (O-2/C) and steam to carbon ratio (H2O/C) at different AIR operating temperatures (700-850 degrees C), while keeping the SOFC stack temperature constant at 910 degrees C. Anode recycle steam and heat have been used to reform the desulfurized JP-8 fuel which would make the system lighter and compact for mobile application. The system modeling revealed a maximum net AC efficiency of 39.5% at 700 degrees C and a minimum of 32.6% at 850 degrees C AIR operating temperatures, respectively. Sensitivity analysis with respect to fuel utilization factor (U-f) and current density (j) were also conducted to identify the optimum operating window. (C) 2012 Elsevier B.V. All rights reserved.