ASEAN Beat | Diplomacy | Southeast Asia

Thailand Unilaterally Voids Maritime Boundary Agreement With Cambodia

The 2001 MoU set up a framework for discussions on joint oil and gas exploration in areas of the Gulf of Thailand claimed by both sides.

Thai Prime Minister Anutin Charnvirakul speaks at a press conference announcing the results of a crackdown on organized crime networks in Bangkok, Thailand, Apr. 30, 2026.

Thailand has cancelled a longstanding agreement with Cambodia over joint offshore energy exploration in the Gulf of Thailand, a move likely to worsen further the relations between the two estranged neighbors.

Signed in 2001, the memorandum of understanding – often referred to as “MoU 44,” after the Buddhist calendar year 2544 – set up a framework ​for discussions on joint oil and gas exploration in areas of the Gulf where the two countries’ maritime claims overlap, and for the demarcation of maritime boundaries.

The ⁠withdrawal, which was approved by the Thai cabinet on Tuesday, has long been expected. Prime Minister Anutin Charnvirakul made it a key campaign promise ahead of the general election in February, when he was decisively re-elected after harnessing the nationalistic sentiment that was uncorked by last year’s border dispute with Cambodia. The dispute erupted into armed conflict on two occasions in 2025, displacing hundreds of thousands on both sides of the border and pushing relations to their lowest point in decades.

Speaking to reporters on Tuesday, however, Anutin denied that the cancellation of the MoU had anything to do with the border conflict. Instead, he cited the lack of headway negotiations with Phnom Penh, saying that “it has been 25 years and there has been no progress.”

The 26,000-square-kilometer Overlapping Claims Area (OCA) in the Gulf of Thailand is believed to contain significant deposits of oil and gas, and the MoU stated that it was “in the best interests of the two countries to agree upon an early mutually acceptable basis for exploration of the hydrocarbon resources of the [OCA] as soon as possible.” The agreement also pledged both sides to “agree upon a mutually acceptable delimitation of the territorial sea, continental shelf, and exclusive economic zone” within the OCA.

Anutin is right that there has been little progress on the talks, although a large part of the reason is the chronic instability in Thai domestic politics. The MoU has long been opposed by Thai nationalists who, nurturing resentments about colonial-era territorial amputations, have argued that the two agreements hamstring Thailand’s ability to assert and defend its sovereign claims.

The most recent illustration of this took place just prior to the recent conflict, when the governments of Prime Minister Paetongtarn........

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