The effect of the quality of ebullated bed vacuum residue H-Oil hydrocracking gas oils cracked in a commercial fluid catalytic cracking unit (FCCU) on its performance was studied. Six different catalysts were employed in this study. Four catalysts were tested in a commercial FCCU, and two in a laboratory FCCU. An increase of the H-Oil hydrocracker reaction temperature was associated with a decrease in theK(W)factor of the H-Oil gas oils. The diminishedK(W)factor of H-Oil gas oils resulted in lower FCCU conversion and higher regenerator temperatures. The FCC conversion at maximum gasoline yield is best predicted by the feedK(W)factor. The higher-activity, higher-Delta coke catalyst is unfavorable for FCCU performance because the excessive regenerator temperature excursions require reduction of the throughput.