Hydrogen sulphide (H2S)-fuelled solid oxide fuel cells (SOFCs) can potentially generate useful electrical energy while disposing of H2S, a toxic by-product of the fossil fuel industry, on site. Experimental results from H2S fuelled SOFCs exhibit characteristics, for example, an unusual dependence of cell performance on fuel composition and flow-rate, which are poorly explained in the literature. In this work we: (a) present results for experiments where the composition and flow-rates were varied for both the fuel and oxidant streams to analyse their effect on fuel cell performance, and (b) develop and use a thermodynamic analysis to help understand these experimental results. Through this work, we shed further light on two basic questions unanswered so far, (1) Why does the flow-rate of the fuel affect the open circuit potential of the fuel cell? (2) Which of the chemical species present in the fuel is oxidised on the anode? Our experiments and analysis suggest that H2S, and not H2 produced from H2S dissociation, is preferentially electro-oxidised on the anode in our experiments. (C) 2011 Canadian Society for Chemical Engineering