This paper investigates the performance of ethanol-fuelled solid oxide fuel cells (SOFCs) with two types of solid electrolytes, namely oxygen ion-conducting (SOFC-O2-) and proton-conducting electrolytes (SOFC-H+). Our previous work reported that the SOFC-H+ shows superior theoretical performance over the SOFC-O2- electrolyte. However, in this work when all resistances are taken into account, the actual performance of the SOFC-O2- (Ni-YSZ/YSZ/YSZ-LSM) becomes significantly better than that of SOFC-H+ (Pt/SCY/Pt). The maximum power density of the SOFC-O2- is about 34 times higher than that of the SOFC-H+ when operated at an inlet H2O:EtOH ratio of 3, a fuel utilization factor of 80% and a temperature of 1200 K. Then the required values of the total resistance of the SOFC-H+ to achieve the same power density as the SOFC-O2- were determined. It was found that due to the superior theoretical performance of the SOFC-H+, it is not necessary to reduce the SOFC-H+ total resistance to the same values as the one for SOFC-O2-. The study also indicates that reduction of only the electrolyte resistance is not sufficient to improve the SOFC-H+ performance and, therefore, the other resistances including activation, electrodes and interconnect resistances need to be reduced simultaneously. Finally, the improvement of the electrolyte resistance by changing its resistivity and thickness is discussed. (C) 2007 Elsevier B.V. All rights reserved.