Unlike PEMFCs, SOFCs can be operated with the CO-containing reformate generated from reformers. In these systems, the performance of SOFCs and reformers is affected by the reforming conditions which can change the flow rate and the composition of the reformate. The SOFC cell voltage increased with the gas hourly space velocity (GHSV) of the diesel autothermal reformer, because of SOFC's lower fuel utilization at the anode, in spite of the decrease of H(2) and CO partial pressures in the reformate. on the other hand, for the changes of H(2)O/C- and O(2)/C-ratio of the reformer, the cell voltage followed the Nernst-voltage tendency. With degrading the reforming performance, large quantities of hydrocarbons were generated, which can lead to coke formation at the anode of SOFC as well as at the reformer. In the case of CH(4), the most abundant hydrocarbon species in the reformate, there was no problem when appropriate amounts of H(2)O were supplied to the anode with CH(4). However, other light hydrocarbons, such as normal butane (nC(4)H(10)), resulted in severe coke formation at the carbon-free condition for CH(4)-direct internal reforming (DIR). The butane DIR system seems to require more water for no-coke conditions than CH(4)-DIR systems do. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.