Idemitsu Family Debuts on Japan’s Richest List at $1.15 Billion as Company Boosts Fossil-Fuel Investments

The family behind oil refiner Idemitsu Kosan entered Forbes’ Japan’s Richest 2026 list at No. 15 billion. Board member Masakazu Idemitsu represents the family on the company’s board.

He is the grandson of founder Sazo Idemitsu, who began selling fuel for fishing boats in 1913. 1 billion, for the year ended March 31, 2026. That figure marked an increase of more than 65% from the prior year.

Shares of the company rose nearly 50% over the past year amid higher crude prices. In March 2026 the company agreed to pay $500 million for an undisclosed stake in London-based MidOcean Energy. The acquisition gave Idemitsu Kosan exposure to LNG projects in Australia, Canada and South America.

8 trillion through 2030. More than half of the funds are allocated to its fossil fuels business. Forbes reported the family’s debut on the list alongside four other new entries.