An improved chemical looping combustion (CLC) process and system includes a hopper containing oxygen carrier particles, e.g., metal oxides, that are gravity fed at a controlled rate of flow from the hopper into (a) a generally vertical downflow reactor where they are mixed with all of the hydrocarbon fuel feed to the system and (b) into one or more standpipes that are in communication with a plurality of staged fluidized reactor beds, the amount of the oxygen carrier particles introduced into the system being stoichiometrically predetermined to produce a syngas mixture of H2 and CO2; or to complete combustion of the fuel to CO2 and water vapor, thereby permitting capture of a majority of the CO2 produced in an essentially pure form.