Two oxygen carriers were tested with respect to chemical looping combustion (CLC) and chemical looping gasification (CLG). Ilmenite, a natural ore composed mainly of iron–titanium oxide, and LD Slag, an iron-based industrial waste, were investigated at 850 and 900 °C in a continuous operation in a 0.3 kW chemical-looping reactor system using synthetic biomass volatiles as fuel. CLC and CLG conditions were simulated in the fuel reactor by changing the fuel flow rates. In the case of ilmenite the syngas yield and methane conversion increased with fuel flow rate. Consequently, the syngas to hydrocarbon ratio was higher for ilmenite. Methane conversion improved for both tested oxygen carriers with increasing the operating temperature. Oxygen release was observed in the case of LD Slag. The H2/CO ratio was between 0.7 and 0.8 for both oxygen carriers at the higher fuel flows. With respect to CLC, ilmenite showed higher gas conversion than LD slag. Analysis of the particles revealed that ilmenite possessed better mechanical properties and formed less dust compared to LD Slag during the continuous operation with fuel.