The influence of hydrocarbon-containing fuel gases on cell performance and coke formation is investigated in this work, wherein acetylene is applied as a model compound for the coke formation. The dependence of coke yield on acetylene amount (volume fraction of 0.05-0.50%) and gas composition is analyzed. Further parameters which are varied are temperature (650-850 degrees C) and operation time. It is shown that the mass of coke that is formed on the cell depends strongly on acetylene volume fraction and temperature. As a consequence, acetylene has a severe influence on the electrical cell performance, and acetylene concentration and temperature can be correlated to degradation effects. (c) 2008 The Electrochemical Society.