The impedance of anode-supported single cells [Ni/8 yttria-stabilized zirconia (YSZ) anode; La0.58Sr0.4Co0.2Fe0.8O3-delta cathode; 8YSZ electrolyte; area 1 cm(2)] was characterized in a broad measuring range of temperature and air/fuel gas composition. The data has been analyzed by calculating the distribution function of relaxation times (DRTs). DRT computations enabled us to separate five different loss mechanisms occurring inside the cathode and anode without the need of an equivalent circuit. Two processes exhibit a systematic dependency on changes in the oxygen partial pressure of the cathode gas and thus can be attributed to diffusional and electrochemical losses on the cathode side. The remaining three processes are very sensitive to changes in the fuel gas but are not affected by variations of the cathode gas. These resistances are classified as a gas diffusion polarization within the anode-substrate and as an electro-oxidation reaction at the triple-phase boundary, respectively. (c) 2007 The Electrochemical Society.