Two different Ni-based oxygen carriers (OCs) are applied to chemical looping combustion (CLC) of natural gas on a scale of 140 kW fuel power. Both OCs are composed of NiO and a support material which is NiAl2O4 in the case of OC-A and a mixture of NiAl2O4 and MgAl2O4 in the case of OC-B. Fuel reactor temperature and global air/fuel ratio variations are performed and indicate the high reactivity of both OCs. Solids sampling during operation allows the determination of the oxidation degree of the particles in the air and fuel reactors. In general, both OCs show a low degree of oxidation during operation. Despite very low H2O/CH4 molar ratios in the fuel reactor, no carbon formation is observed under any conditions. In reforming conditions (global air/fuel ratio < 1), a complete uptake of the available O-2 is observed in the air reactor.