Scrapping Cambodia MOU was easy, but is Thailand ready for UNCLOS intervention?

While Thailand has signaled its intention to scrap the memorandum of understanding (MOU) on maritime claims with Cambodia, the administration under Prime Minister Anutin Charnvirakul appears far less prepared to manage the impending legal, diplomatic and political fallout.

The Thai Cabinet on May 5 resolved to end the MOU signed in 2001 by the Thaksin Shinawatra administration to settle maritime disputes between the two countries and jointly develop hydrocarbon resources in the overlapping claim areas in the Gulf of Thailand.

Unless the Cabinet seeks the opinion of the Constitutional Court on whether the termination of the MOU requires parliamentary approval, the government is supposed to inform Phnom Penh in writing through appropriate diplomatic channels within 12 months, as mentioned in the 1969 Vienna Convention on the Law of Treaties.

Prime Minister Anutin revealed that he had already informed his Cambodian counterpart Hun Manet, when they met on the sidelines of the ASEAN Summit in the Philippines on May 8, and hence there was no need to comply with the Vienna Convention.

“For me, the fact that Cambodia was formally informed of the Thai government’s decision to terminate the MOU during this meeting can be regarded as clear evidence that Cambodia has officially acknowledged Thailand’s decision,” Anutin posted on his Facebook on May 8.

Had this meeting not taken place, the Thai government would have had to notify the Cambodian government in writing, and the process would likely have taken at least six months to conclude, he said.

As his Bhumjaithai Party exploited nationalist sentiment to win the election, it seemed that Anutin had prioritized his political popularity over the legal procedure for terminating the MOU.

Right-wing nationalist groups have long called for termination of the agreement, citing concerns over territorial loss, particularly Koh Kut in Trat province, and the sharing of resources with Cambodia.

“With the termination of MOU 2001, there will no longer be a line passing through Ko Kut Island to create doubt or concern. My fellow citizens can rest assured that #KoKutBelongsToThailand,” Anutin said in a Facebook post with that hashtag.

The overlapping continental shelf in the Gulf of Thailand, claimed by both Thailand and Cambodia since the 1970s, covers approximately 26,000 square kilometers. Studies suggest the area contains sizeable energy reserves, including an estimated 11 trillion cubic feet of natural gas and 300–500 million barrels of crude oil, with a combined economic value of around US$300 billion.

Reset negotiations

Despite the termination of the 2001 MOU, Deputy Prime Minister and Foreign Minister Sihasak Phuangketkeow informed his Cambodian counterpart, Prak Sokhonn, that his government preferred continuing negotiations to settle the bilateral maritime disputes under the framework of the 1982 United Nations Convention on the Law of the Sea (UNCLOS), which has been ratified by both Thailand and Cambodia.

Senior officials at the foreign ministry explained the termination of the MOU had sent a signal to Phnom Penh that Cambodia’s recent ratification of the UNCLOS was offering a new platform for both countries to reset negotiations, considering talks under the 2001 MOU had made no significant progress over the past 25 years.

Compulsory conciliation

The government in Phnom Penh views the UNCLOS differently, and has made it clear that it would enter the compulsory conciliation process under the UN convention.

Prime Minister Hun Manet said Cambodia regretted Thailand’s unilateral withdrawal from the agreement, describing the MOU as the only mutually accepted bilateral mechanism for addressing maritime disputes peacefully.

Cambodia, as a country committed to international law and peaceful dispute settlement, now had no choice but to rely on international law, particularly the compulsory conciliation mechanisms of UNCLOS, he said.

Established under Annex V of the 1982 UNCLOS, compulsory conciliation is a non-binding dispute settlement mechanism designed primarily for complex maritime disputes, including maritime boundary delimitation, where states are unable to reach an agreement through direct negotiations.

Article 12 of Annex V of the UNCLOS will allow Cambodia to unilaterally continue with the conciliation proceedings, as the article stipulates that “the failure of a party or parties to the dispute to reply to notification of institution of proceedings or to submit to such proceedings shall not constitute a bar to the proceedings”.

Diplomatic row

While Prime Minister Anutin and his deputy Sihasak have referred to the UNCLOS several times in public and in meetings with their counterparts, it remains unclear whether Bangkok will agree to enter the conciliation process.

Foreign Minister Sihasak had earlier denied media reports that his government had agreed to enter compulsory conciliation proceedings to settle maritime disputes with Cambodia, citing that various steps must be taken before such a process begins.

Following the cancellation of the 2001 MOU, various negotiation frameworks must be addressed before concluding, he said.

Cambodia’s acting head of state, former prime minister Hun Sen, argued that compulsory conciliation required no negotiation before proceeding with the process.

Sihasak’s words contradicted his own government’s action, according to Hun Sen’s Facebook post. Thailand unilaterally cancelled the MOU 2001, thereby already dismantling the framework for bilateral negotiations concerning the overlapping maritime claims, he argued.

“In my capacity as Acting Head of State, I would like to remind the Royal Government [of Cambodia] not to engage in any bilateral negotiations with Thailand on maritime issues, and instead to proceed directly to the mechanisms provided under the 1982 UNCLOS without waiting for any agreement from the Thai side,” Hun Sen posted on Facebook.

“On May 6, 2026, I already reminded the government once not to create a new bilateral mechanism to replace the old bilateral mechanism that Thailand had cancelled. We regret Thailand’s cancellation of the MOU 2001, but we also thank Thailand for helping us move toward using international mechanisms instead,” Hun Sen, who is the president of the Senate, insisted.

Legal experts in Thailand interpreted the compulsory reconciliation proceedings differently.

While one side agreed with Sihasak, citing Article 298, that the process would not begin before the failure of negotiation in a period of time, others nodded with Hun Sen’s point of view, saying the conciliator commission in the case of Timor Leste and Australia (2016-2018) made clear that Article 298 does not grant a party the right to veto any recourse to compulsory conciliation.