Chemical-looping with oxygen uncoupling (CLOU) is a developing technology, which allows For inherent separation of carbon dioxide during combustion of gaseous and solid fuels. In contrast to the related chemical-looping combustion technology (CLC), where gaseous or gasified fuels react directly with oxygen carrier materials, CLOU utilizes oxygen carriers capable of releasing gaseous oxygen, provided appropriate thermal conditions exist in the Fuel reactor, whereupon fuel reacts with the released oxygen. The oxygen carriers are thereafter regenerated by oxidation in the air reactor. In this work, a set of oxygen carrier materials synthesized from manganese oxides mixed with iron, nickel, and silicon oxides are evaluated in terms of their ability to release oxygen and to be regenerated with oxygen and in terms of demonstrated methane conversion in a quartz fluidized bed batch reactor at 810, 850, and 900 degrees C. The results demonstrate that two Mn/Fe oxygen carriers and one Mn/Ni oxygen carrier have both oxygen release characteristics and high reactivities with methane. The Mn/Fe oxygen carrier synthesized at 1100 degrees C was additionally shown to have ail increasing methane conversion oil a long-term basis, which opens for a possibility to use Mn/Fe oxygen carriers in time-extended large-scale chemical-looping operations.