Chemical looping combustion is an emerging CO2 capture technology. Treatment of a fuel with a metal oxide partially reduces the metal oxide while yielding a waste stream containing only CO2 and H2O. The reduced metal oxide is then oxidized with air to regenerate metal oxide which is returned to the fuel stream to complete the cycle. Chemical looping may be viewed as a variant of oxy-fuel combustion in which a metal oxide to metal transition acts as an oxygen carrier, obviating the expensive process for generating pure oxygen. However, the chemical looping combustion of solid and liquid fuels is much more complicated than the combustion of gaseous fuels. In addition, the fluidized bed reactors needed for combustion and the processes to circulate solids between the combustion chamber and the reoxidation reactor are complex and nontrivial and require significant optimization to reduce operating and manufacturing costs. The above four CO2 capture processes are compared in Table .