The performance of two-cell planar solid oxide fuel cell stacks using coal syngas, with and without hydrogen sulfide (H2S), was studied. All cells were tested at 850 °C with a constant current load of 15.2 A (current density of 0.22 A cm-2 per cell) and 30% fuel utilization. The H2S injection immediately and significantly affected the power degradation of the stack system regardless of the carrier fuel. Results for the test with only H2 and N2 in the presence of H2S (119-120 ppm) indicated that the power decay and area-specific resistance (ASR) degradation values were lower than those for the tests where simulated syngas containing CO and increased water content was used. The results indicate that contact points in the stack contributed to the power degradation of the system. Other factors, including contamination from the upstream fuel gas tubing, may have contributed to the higher degradation under simulated syngas conditions. In general the data confirm previous results for single cell testing, and showed that for this specific short stacks (two-cells) arrangement both a fast and a slow response to H2S injection that eventually stabilized. © 2006 Elsevier B.V. All rights reserved.