The aim of this study was to evaluate limiting factors affecting electricity output from sediment microbial fuel cells (sediment MFCs). In laboratory tests, various factors likely to be encountered in field application were divided into controllable and uncontrollable ones. Based on the findings, it could be suggested that the sediment MFCs can be operated with an anode to cathode area ratio of at least 5:1 and at high external loads (1000 Omega) when the cathode is closely placed to the anode, though DO concentration at the cathode must be kept above 3 mg/l. Furthermore, no significant effect on current production over a prolonged period was observed within the sediment temperature range of 20-35 degrees C, but was negatively affected by lower temperatures (10 degrees C). These observations provide important factors with respect to the construction and operation of sediment MFCs at field sites, which will aid in maximizing electricity output. (C) 2009 Elsevier Ltd. All rights reserved.