[en] Highlights: • 4 different oxygen carriers have been tested in a 120 kW_t_h CLC pilot plant. • Oxygen carriers are divided into 3 different Groups. • 6 oxygen carriers are sorted into the 3 Groups. • Demands of the 3 Groups on the CLC reactor design are highlighted. - Abstract: Chemical looping combustion is now at a point beyond proof of concept. Lots of different oxygen carriers have been developed using different metal oxides, support materials and production methods. The interchangeability of oxygen carriers in a chemical looping combustion plant is investigated in a 120 kW_t_h pilot. Four different oxygen carriers are tested with focus on reactor temperature, total solids inventory, specific fuel reactor inventory, solids circulation rate and air to fuel ratio. The experimental data of this work, the data of previous work with the same pilot plant and thermodynamic data allow the identification of three groups of oxygen carriers according to the demands on the reactor system for good fuel conversion. Different reactor configurations and potentially limiting factors for each type of oxygen carrier are identified. Changing oxygen carriers of the same group in an existing chemical looping plant seems to be possible without big changes of the reactor configuration.