Chemical looping combustion (CLC) is an indirect combustion process in which a carbonaceous fuel is combusted without direct contact with air. Rather, transfer of oxygen between air and the fuel takes place with the aid of an oxygen-carrier (OC) material, yielding a CO2 stream of very high purity. This process is attractive for CO2-capture applications because it does not require additional energy to separate CO2 from N-2, as in postcombustion CO2-capture processes. In this work, a mass and energy balance model has been developed to estimate the performance of a CLC system using different OC materials. To simplify the calculations, the specific heats of all gases and solids were assumed to be constant over the range of temperatures considered. The model was then applied to evaluate the effects on system performance of several design and operating parameters using three different OC materials. Given input conditions such as fuel, reactor operating temperature, fuel and OC material, the model calculates the amount of OC required and the resulting temperature and system flow rates. The model can be applied to any gaseous fuel containing CH4, CO, and H-2. The CLC model, coupled with a plant-level systems model, was used to evaluate the performance of a conceptual CLC-based natural gas combined-cycle (NGCC) power plant, using three different OC materials. Two configurations were studied for each case: (1) the low-pressure heat-recovery steam generator (LP-HRSG) case, where the flue gases from the fuel reactor are first expanded in an expander and then sent to a CO2 compressor after the water vapor has been condensed, and (2) the high-pressure HRSG (HP-HRSG) case, where the flue gases are cooled at high pressure and the CO, is compressed after the water vapor has been condensed. In general, the power output and efficiency [>50%, on the basis of higher heating value (HHV)] of the CLC-NGCC plant were found to be comparable to or higher than those of a conventional NGCC power plant without CO, capture and storage (CCS), whose net plant efficiency is close to 50% (HHV). The LP-HRSG configuration was found to have a higher net power output (about 10 MW) and net plant efficiency (about 2 percentage points) than the HP-HRSG configuration. Among the three OC materials, Ni-OC systems gave slightly better performance than Fe-OC and Cu-OC systems. Considering that CO2 capture is inherent in CLC-NGCC plants, CLC appears to be a highly competitive CO2-capture technology, at least in terms of overall plant performance.