Fossil fuels are still used to meet the worldwide energy demand. The combustion of fossil fuels increases the concentration of carbon dioxide in the atmosphere, one of the main causes of climate change. A method to reduce carbon dioxide emissions is Carbon Capture and Storage (CCS). Especially in the area of capturing CO2, however, many technologies are still under development. Chemical Looping Combustion (CLC) has shown to be a promising capture technology, keeping the energy demand for separation of CO2 low. A CLC system consists two reactors, the so-called air reactor (AR) and the fuel reactor (FR). Between the two reactors, a metal oxide is circulating which is responsible for oxygen transport from AR to FR. These oxygen carriers are oxidized with air in the AR and then reduced by the fuel in the FR. This results in two separate exhaust gas streams. On the one hand, there is the oxygen-reduced air from the AR and, on the other hand, carbon dioxide with water vapour in the FR. After separating the steam, a highly concentrated CO2 stream is available. One of the challenges in CLC is to find a metal oxide that is suitable as an oxygen carrier. First experiments were performed with a nickel-based oxygen carrier and yielded promising results. Subsequently, research has been conducted with alternative oxygen carriers, mainly because of the high environmental risks and costs associated with nickel. A new material for CLC coming from the field of fuel cells are perovskites. Perovskites consist of several elements and form a structure that is able to absorb and release oxygen. These materials are assigned to the category of CLOU - oxygen carriers (Chemical Looping with Oxygen Uncoupling). Two of these materials, C14 and C28, were developed in the EU FP7 project INNOCUOUS. The stoichiometric composition of the C14 is CaMn0.9Mg0.1O3- and of the C28 CaMn0.775Mg0.1Ti0.125O3-. In the course of this thesis, the performance of these two oxygen carriers was tested at the existing 120kWth CLC test unit of the TU Wien. Parameter variations were carried out in order to examine the influence of temperature, inventory, power, fuel type and air to fuel ratio, on the process. During a period of more than 40 CLC operating hours, a total amount of 75 operating points was obtained, evaluated and presented in this master thesis. It was shown that full conversion of the used fuel is possible with both oxygen carriers. Temperature, air to fuel ratio and specific inventory were the main factors of influence. Higher temperatures had a positive effect on fuel conversion. The air to fuel ratio has an influence on the oxygen concentration in the AR and the solids circulation rate. It could be shown that a higher air to fuel ratio has a positive effect on the conversion of methane. In order to investigate the influence of oxygen concentration in the AR at a constant solids circulation rate, the air in the AR was gradually substituted with nitrogen. This allowed to vary the air to fuel ratio and keep the solids circulation constant. This dilution with nitrogen was carried out with both oxygen carriers and proved that the partial pressure of oxygen in the AR has decisive influence on the fuel conversion. Furthermore, the two oxygen carriers were examined more closely using the following measurement methods: X-ray fluorescence spectroscopy (XRF), thermal gravimetric analysis (TGA), scanning electron microscope (SEM) and particle size distribution. These analyses were conducted with both fresh and used material. Fresh material showed a higher elutriation during the first operating hours, whereas the elutriation decreased with operating time. Besides, a modification of the grain size distribution could be detected. The element structure did not change during the experiments which can be attributed to their structure and the way of production. The two oxygen carriers showed great performance in the 120kWth CLC test unit. The oxygen carrier C28 proved to have better reactivity, which made it possible to improve the fuel conversion. The C14 showed better mechanical strength, which led to a lower elutriation.