Spray-dried particles with the chemical compositions of Fe0.66Mn1.33SiO3 and FeMnSiO3 have been examined as oxygen carrier materials for chemical-looping combustion. The experiments were carried out in a fluidized-bed reactor system designed for a thermal power of 300W. Both materials were able to release gas phase oxygen in inert atmosphere at temperatures between 800 and 950 degrees C, and with approximately equal oxygen concentrations. Fe0.66Mn1.33SiO3 provided higher conversion of natural gas as compared to FeMnSiO3 and the fuel conversion increased with temperature for both materials. During natural gas operation with Fe0.66Mn1.33SiO3 the conversion reached 100% at around 950 degrees C with a fuel reactor inventory of 235 kg/MW. The fuel conversion improved when the solid inventory was increased; this improvement could especially be observed for FeMnSiO3 as the fuel conversion was lower for this material. Fe0.66Mn1.33SiO3 also provided higher fuel conversion than FeMnSiO3 when syngas was used as fuel. The fuel conversion increased with temperature for both materials and full conversion was reached above 800 degrees C with a fuel reactor inventory of 225 kg/MW for Fe0.66Mn1.33SiO3, while FeMnSiO3 was incapable of providing full conversion. A rather large elutriation of fines and a significant change in particle size distribution could be observed during operation for both materials. (C) 2014 Elsevier B.V. All rights reserved.