Thailand says that it will join a U.N. arbitration ​process to resolve a maritime boundary dispute with Cambodia, but expressed regret at Phnom Penh’s decision to seek international mediation for the dispute.

Last week, Cambodia officially notified Thailand that it was seeking compulsory conciliation under the United Nations Convention on the Law of the Sea (UNCLOS) to resolve a long-running maritime border dispute in the Gulf of Thailand. This came after Bangkok unilaterally withdrew from a 2001 agreement with Cambodia that established a framework for joint offshore energy exploration and the demarcation of maritime boundaries in the area.

Speaking to reporters in Bangkok on Friday, Thai Foreign Minister Sihasak Phuangketkeow said that Thailand would appoint two conciliators to take part in the process, but expressed dismay at Cambodia’s decision to seek conciliation.

“Both sides should have spoken bilaterally first,” Sihasak said. “If we had talked and there was no progress, then we could go to UNCLOS.”

In separate comments to Reuters, the Thai foreign minister added that as long as the UNCLOS process was moving forward, Bangkok would not hold any other two-way talks. This includes efforts to manage and resolve the ongoing disputes over the land border, which erupted twice into armed conflict last year.

“We will use UNCLOS, which means ​from now on there will be ​no more talks … or other forms ⁠of cooperation,” he told the news agency, adding that all of the border gates between the two nations would remain closed. “We will not discuss the restoration of relations yet,” Sihasak said.

However, Thailand’s call for bilateral talks is undermined somewhat by its decision to withdraw from the 2001 MoU. This was specifically set up to provide a framework for negotiations between Phnom Penh and Bangkok over a 26,000-square-kilometer area in the Gulf of Thailand that is known as the Overlapping Claims Area (OCA). The OCA, which has been disputed since the early 1970s, is estimated to hold abundant reserves of oil and natural gas, the exploitation of which has become more pressing amid the current global oil supply crisis.

In announcing the decision to withdraw from the agreement last month, Prime Minister Anutin Charnvirakul cited the lack of progress in the talks under the MoU. However, a major reason for this lack of progress is the chronic instability in Thai domestic politics. The 2001 MoU has long been opposed by Thai nationalists, who argue that it could lead to the loss of Thai sovereignty over Koh Kood, a small island in the Gulf of Thailand. Indeed, tensions over the question of Koh Kood led to the collapse of bilateral talks on the OCA in late 2024, arguably contributing to the resumption of the dispute over the land border in the first half of 2025.

Last week, I expressed some skepticism that Thailand would join the process under UNCLOS, citing its long preference for bilateral negotiations. Last year, Thailand rejected Cambodia’s decision to take four areas of the disputed land border to the International Court of Justice (ICJ), which twice ruled in favor of Cambodia in the case of Preah Vihear temple, in 1962 and 2013.

However, Thailand’s Ministry of Foreign Affairs, which reportedly opposed the scrapping of the 2001 MoU, is evidently concerned about the reputational impacts of a decision to flout UNCLOS. While Thailand has refused the ICJ’s jurisdiction since the early 1960s, and still contests its ruling over Preah Vihear, to thumb its nose at a major international treaty that it ratified as recently as 2011 would undermine Thailand’s desire to present itself as an international citizen in good standing, as well as possibly mobilizing sympathy for Cambodia’s position.

Whatever its motivation, and leaving aside its decision to freeze other bilateral talks, Thailand’s decision to participate in compulsory conciliation is a positive development. Given the dire state of relations between the two sides, any opportunity to discuss outstanding boundary issues with impartial mediators, especially in a venue insulated from nationalist constituencies back home, is worthwhile.

Whether or not this results in a resolution of the maritime border, which is rooted in differing interpretations of the 1907 Franco-Siamese Treaty, remains highly uncertain.

Under compulsory conciliation, each country will appoint two independent experts – known as conciliators – to a special commission, which will then select a fifth member to act as chair. The commission will then investigate the facts of the case and the legal position of ​each state and deliver a set of non-binding recommendations. However, these recommendations are not legally binding on either party.

In principle, there is no reason why the two sides could not reach a compromise on the OCA, based on or around the median line of their respective claims. Given the crisis in the Middle East, they both certainly have an interest in pressing ahead with joint exploration of the oil and gas resources lying within the disputed area.

However, when the conciliation commission releases its non-binding recommendations, politics would re-enter the picture. At that point, it would be up to both governments to sell the commission’s solution to prickly nationalist constituencies that tend to view even reasonable compromise in the most suspicious light.

Being able to do so would be very unlikely in the current circumstances. While Thailand and Cambodia agreed to a ceasefire in late December that ended the conflict on their land border, tensions remain high both on land and at sea. These seem unlikely to abate for the foreseeable future, especially given that Thailand has foreclosed the possibility of bilateral talks while the UNCLOS process plays out. Absent a marked improvement in relations between Bangkok and Phnom Penh, the conciliation commission’s recommendations will likely be dashed against the rocks of domestic politics.