In response to the Suez Canal Incident of 1956, shipbuilders began constructing mammoth tankers with capacities of 66,000 tons or more, which could be competitive even when traveling over routes via Capetown. Starting with the Universe Admiral (85,000-ton capacity) in 1956, Idemitsu then went on to build the third-generation Nissho Maru, at the time the world's largest tanker with a capacity of 139,000 tons.
Construction of Mammoth Tankers

The third-generation Nissho Maru nears completion
Also, in August 1962 Idemitsu Tanker was established in the international tanker business, as Idemitsu began full-fledged participation in the maritime shipping business for the first time since the war. In December 1966, the Idemitsu Maru (209,000-ton capacity), the world's first 200,000-ton-class very large crude carrier (VLCC) was commissioned.
Together with securing a stable supply of crude oil through using its own vessels, Idemitsu's construction of large tankers also contributed to the development of the shipbuilding industry in Japan.

Attaching the screw propeller to the Idemitsu Maru
- Idemitsu Shokai Founded in Moji
- Overseas Branches Closed, Repatriation Begins
- Importing High-Octane Gasoline from the United States
- The Nissho Maru Incident: Challenging the Dominance of the Major Oil Firms
- Construction of Mammoth Tankers
- Completion of the Tokuyama Refinery
- Chiba Refinery Completed/Idemitsu Withdraws from the PAJ
- Idemitsu Enters the Oil Exploration and Production
- The First Oil Crisis and Advancing Overseas
- Specific Petroleum Law Abolished
- The Establishment of Idemitsu Credit and Development of the Credit-Card Business
- Outbreak of the Gulf War
- Introduction of Low-Benzene Gasoline