A fuel reactor with a fuel-injection system for liquid fuels was designed and built for a chemical-looping reactor system with the nominal fuel input of 10 kW(th). The gas velocities in the riser section and at the gas-distribution nozzles of this unit are comparable to those of industrial circulating fluidized-bed boilers. Proof-of-concept experiments were performed with a calcium manganite-based oxygen carrier and a fuel oil with low sulfur content. Fuel conversion was high but not complete, and most of the fuel carbon was converted to CO2 in the fuel reactor. Long-term experiments were performed using an ilmenite oxygen-carrier. The oxygen carrier was exposed to fluidization at hot conditions (more than 600 degrees C) for about 204 h, out of which fuel was injected during a total of 66.6 h. The parameters temperature, fuel flow, steam flow in the fuel reactor, fluidization medium in the fuel reactor, and air flow in the air reactor were varied to observe trends in fuel conversion. Most of the experiments were carried out with a fuel flow corresponding to 4 kW(th) and an oxygen carrier-to-fuel ratio of about 2100 kg/MWth. At 1050 degrees C the fuel could be oxidized to about 87%, and up to 88% of all carbon leaving the fuel reactor was in the form of CO2. No defluidization or agglomeration problems were experienced over the course of the experimental campaign.