An integrated fuel cell system consisting of a fuel processor for diesel and kerosene and high-temperature polymer electrolyte fuel cell (HT-PEFC) stacks was developed and tested. This paper reports on the operational experience from system tests with different middle distillates. The key components, the autothermal reformer and the HT-PEFC stack, showed robust performance during system tests. An electrical peak power of 5.56 kW was reached in the system. Performance losses were observed for the water-gas shift reactor as well as for the catalytic burner. Due to the limited partial load capability of the reformer, the system was operated with constant reformer load. As a consequence, the hydrogen utilization of the stack was rather low at partial load operation of the system. The target hydrogen utilization of 83% was realized at the target maximum system power of 5 kW.