This invention relates to efficiently regenerating catalyst particles by minimizing the formation of localized "hot spots" and "cold spots" in a regeneration zone. In one embodiment, the invention includes mixing spent catalyst from a reactor and cold catalyst from a catalyst cooler in a mixing zone and directing the mixed catalyst to the regeneration zone in a fluidized manner with a fluidizing medium. In the regeneration zone, the mixed catalyst contacts an oxygen-containing regeneration medium under conditions effective to regenerate the spent catalyst contained therein.