At the stage of the IMCO draft text for segregated ballast tanker, 1973, the volume of segregated ballast tanks was based on deadweight, and smaller draft compared with conventional tanker was obtained as the optimum one. But the volume of segregated ballast tanks was finally so decided as to satisfy the requirement for the draft of ballast condition, and on the contrary, it was concluded that the optimum draft of the segregated ballast tanker is deeper than that of the conventional tanker.