single chamber solid oxide fuel cells, SC-SOFCs, design and performance is discussed. It is shown that all of them operate on non-selective anodes. They operate on cathodes that become selective only under short residence times. As a result these cells are not functioning as true mixed reactant solid oxide fuel cells (MR-SOFC). The lack of selectivity is a serious draw back. True MR-SOFC can be constructed in ways that make them cheaper in fabrication, providing high power density, high fuel utilization and reduced explosion risk. The fact that SOFCs operate in a single cell is a necessary but not sufficient condition for the proper operation of MR-SOFCs. The selectivity looked for the anode and cathode is of a special kind. It selects between electrochemical and chemical reactions, preferring the first ones. Results reported here suggest that MR-SOFC can operate only up to similar to 600 degrees C. At these relative low temperatures, materials other than oxides can also be considered for use. Future directions in the needed research in order to develop true MR-SOFCs are discussed. (C) 2007 Published by Elsevier B.V.