A high temperature (700-900 degrees C) SOFC with yttria stabilized zirconia (YSZ) solid electrolyte was constructed and tested on direct feed of simulated biogas (CH4+CO2) mixtures. Both catalytic, i.e. open-circuit, and electrocatalytic, i.e. closed-circuit, measurements were carried out. Open-circuit kinetic data showed that the rate of the catalytic reaction of the dry(CO2)-reforming of methane is maximized at about equimolar CO2/CH4 feed ratio for all temperatures studied. Closed-circuit data showed that cell output characteristics (i.e. current and power densities) are also maximized for equimolar CO2/CH4 biogas composition. Power densities up to 51.6 mW/cm(2) (at V=453 mV, i=114 mA/cm(2), T=875 degrees C) have been obtained. Long-term operation experiments demonstrated that the constructed biogas fuel cell has very stable behavior for all three different simulated biogas compositions fed, including poor, equimolar and rich methane constitutions. (c) 2006 Elsevier B.V. All rights reserved.