In the present work, mathematical models of indirect internal reforming solid oxide fuel cells (IIR-SOFC) fueled by methane were developed to analyze the thermal coupling of an internal endothermic reforming with exothermic electrochemical reactions and determine the system performance. The models are based on steady-state, heterogeneous, two-dimensional reformer and annular design SOFC models. Two types of internal reformer i.e. conventional packed-bed and catalytic coated-wall reformers were considered here. The simulations indicated that IIR-SOFC with packed-bed internal reformer leads to the rapid methane consumption and undesirable local cooling at the entrance of internal reformer due to the mismatch between thermal load associated with rapid reforming rate and local amount of heat available from electrochemical reactions. The simulation then revealed that IIR-SOFC with coated-wall internal reformer provides smoother methane conversion with significant lower local cooling at the entrance of internal reformer. Sensitivity analysis of three important parameters (i.e. flow direction, fuel inlet temperature and operating pressure) was then performed. IIR-SOFC with conventional counter-flow pattern (counter-flow of air and fuel streams through fuel cell) was compared to that with co-flow pattern. it was found that IIR-SOFC with co-flow pattern provides higher voltage and smoother temperature gradient along the system. Lowering the fuel inlet temperature results in smoother temperature profile at the entrance of the reformer, but leads to the increase in cell overpotentials and consequently reduces the cell voltage. Lastly, by increasing operating pressure, the system efficiency increases; in addition, the temperature dropping at the entrance of internal reformer is minimized. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.