Based on previous long-term SOFC stack tests, two short stacks (one F20 and one F10 design) were tested in order to investigate stack performance under high fuel utilization (>40%) and possibly also high current densities (>0.5 Acm(-2)). The F20-design stack was still operated with relatively mild current densities (<= 0.5 Acm(-2)), but with high fuel utilization of up to 90% with 10% pre-reformed liquefied natural gas (LNG). The F10-design stack was operated with 20% humidified H-2, but with high fuel utilization of up to 90% and high current densities of up to 1.5 Acm(-2). Preliminary analysis shows that both F10- and F20-design stacks can be operated smoothly at a fuel utilization of similar to 85% in the temperature range of 750 similar to 800 degrees C, although an increase in concentration polarization can already be observed at the fuel utilization of similar to 80%. Operation with fuel utilization of 90% led to local oxidation of cells at a similar position in both stacks. Based on the calculations with a 1D model, such an effect was assumed to be due to the variation in fuel utilization caused by the temperature gradient in the cell. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.