1969 Jul.

Established by 17 Mitsui Group companies

1969 Oct.

Acquired shares of JAPEX Indonesia, Ltd., (current INPEX) from Mitsui & Co., Ltd.

1970 Sep.

Succeeded an interest in Gulf of Thailand from Mitsui Mining Co., Ltd.​

1974 Sep.

Succeeded concessions in Hokkaido from Mitsui Mining Co., Ltd.

1977 Apr.

Opened the Bangkok Office​

1978 Jan.

Participated in an oil production project in Indonesia​

1981 Aug.

Started the production of natural gas and condensate in Gulf of Thailand​

1983 Jun.

Moved to Hibiya Central Bldg. ​

1990 Feb.

Thai offshore gas sales reached a total of ​1 trillion cubic feet​

1990 Apr.

Merged with SouthEast Asia Petroleum Exploration Co., Ltd.

1996 May.

Acquired an interest in Vietnam

2002 Jun.

Participated in an oil production project ​in Oman​

2004 Jan.

Started an operator project in onshore Thailand​

2005 Aug.

Participated in an oil production project in Gulf of Thailand​

2010 Mar.

Participated in a Shale Gas project in onshore U.S.​

2012 Jun.

First oil production from the operator project in onshore Thailand​

2012 Dec.

Participated in the geothermal business​
Participated in a North Sea production project in UK​

2013 Jun.

Participated in an oil development project in Italy​

2013 Sep.

Acquired an interest in Myanmar​

2015 Dec.

Acquired an interest in Brazil​

2016 Nov.

Participated in an oil development project in the U.S. Gulf of Mexico (“Kaikias Deep-water project”)

2017 Nov.

Acquired an interest in Malaysia​

2018 May.

First oil production from the Kaikias ​Deep-water project the U.S. Gulf of Mexico​

2018 Aug.

Acquired an interest in onshore Indonesia​

2019 Dec.

First oil production for the Tempa Rossa Project in Italy​

2020 Nov.

Moved to Otemachi One Mitsui&Co. Building​(current Head Office)

2022 Mar.

Became 100% subsidiary of Mitsui & Co.

2022 Apr.

Expiry of the concession agreement for the Erawan project, offshore Thailand

2022 Dec.

Withdrawal from Myanmar projects

2024 Mar.

Final investment decision for the Vietnam Block B Project

2025 Jan.

Changed company name to Mitsui Energy Development Co., Ltd.