It is well known that a submarine has the excellent propulsive performance in high speed. navigation in deeply submerged condition, but few papers have sufficiently shown economical feasibility of submarines for commercial use. The authors have studied about the feasibility of submarine tankers with a view to develop technical problems of commercial submarines. At first, the experiments on five submarine tanker models with the circular and rectangular hull sections were performed by method of three-component measurements at Mejiro No. 2 Tank. Examining the resistance, stability, floating draft and general arrangement of the submarine tankers, the authors chose the ST-2 type rectangular hull form as best for the submrine tanker. The lines of the ST-2 type hull form was shown in Fig. 3 The ST-2 type submarine tankers with various dead weights and shaft horse powers were designed and their investment, operation cost, annual profit, freight rate per dead weight and capital recovery factor were calculated. The results of this study were summarized in Fig. 19 to 23. The best submarine tanker in the point of view of commercial feasibility was 40, 000 tons in dead weight and 20, 000 horse powers in shaft horse power under restrained condition within 14 meters in maximum floating draft. On the contrary to the previous opinions, was shown the fact that the submarine tankers would not be very fast than present conventional tankers. As shown in Fig. 23, the submarine tanker would not have commercial feasibility without drastically decreased cost of nuclear power plants.