After it had been found that the barrier layer was permeable to the electrolyte during the growth process the possibility was analyzed that the electrical breakdown of the barrier layer is the rate determining step during the steady-state growth of the porous oxide on aluminum as part of a discontinuous mechanism suggested in 1983. The porous oxide growing on aluminum in the steady-state was treated as a succession of barrier layers which are formed and transformed one after another by three essential steps. No discordant fact has been found to contradict the supposition that the electric breakdown of the barrier layer is the rate determining step of the porous oxide growth.