In this paper Mr. Katayama of the Idemitsu Tanker Company describes some of the advantages and problems of operating mammoth tankers. The size of average tanker tonnage over the past seven years has increased from 33,000 to 55,000. The paper first of all discusses the economic advantages of large tankers and then describes the limiting factors to size, both from a shipbuilding and operating point of view. The handling and manœuvring characteristics of the Nissho-maru, the world's largest tanker which is operated by the author's company, are then described, and finally some navigational details of the passages made by this ship are given.