The performances of solid oxide fuel cells (SOFCs) fed by different types of feed, i.e. biogas, biogas-reformed feed, methane-reformed feed and pure hydrogen, are simulated in this work. Maximum temperature gradient and maximum cell temperature are regarded as indicators for operation viability investigation whereas power density and electrical efficiency are considered as performance indicators. The change in operating parameters, i.e. excess air, fuel feed rate and operating voltage, affects both the performance and operation viability of SOFC, and therefore, these operating parameters should be carefully selected to obtain best possible power density and reasonable temperature and temperature gradient. Pure hydrogen feed offers the highest SOFC performance among the other feeds. Extremely high excess air is required for SOFC fed by biogas to become operation viable and, in addition, its power density is much lower than those of SOFCs fed by the other feeds. Methane-reformed feed offers higher power density than biogas-reformed feed since H-2 concentration of the former one is higher. (C) 2009 Elsevier B. V. All rights reserved.