Thailand and Cambodia at UNCLOS: where they stand on maritime dispute

Thailand and Cambodia have held the first compulsory conciliation meeting over their maritime dispute in the Gulf of Thailand. Their opening statements offered key clues about how each side frames the dispute and what they may seek from the process.

The first three-day session (14-16 September) of compulsory conciliation under the United Nations Convention on the Law of the Sea (UNCLOS) between the two countries was held in Singapore, with Cambodia and Thailand exchanging opening statements on 15 September. 

Cambodia does not rule out possibility of a joint development area

Prak Sokhonn, Cambodia’s Minister of Foreign Affairs and International Cooperation, began with Cambodia’s history and its commitment to a peaceful resolution in accordance with international law. 

He said that Thailand unilaterally terminated the 2001 MOU in May. With its commitment to peaceful settlement of the dispute, Cambodia chose to initiate compulsory conciliation under UNCLOS. “Cambodia sees this conciliation process as a means to rebuild trust, not a form of escalation,” said Prak Sokhonn. 

Cambodia also hopes that Thailand will engage constructively and will work to implement all existing bilateral agreements, particularly the 27 December 2025 joint statement, This would facilitate the return of 20,000 displaced villagers to their homes and the preservation of cultural sites which have been damaged in the fighting.

Cambodia’s objective in the proceedings is to conclude a treaty with Thailand in order to delimit a single all-purpose maritime boundary. Alternatively, Cambodia would be prepared to conclude an agreement on the joint development and equitable sharing of resources with Thailand, pending a final agreement on the maritime boundary.

If a final agreement on either the maritime boundary or a joint development arrangement cannot be concluded, Cambodia would request the commission to prepare a report containing recommendations to the parties for further settlement.

Thailand eyes ‘maritime boundary delimitation’ only

In his statement, the Thai Foreign Minister Sihasak Phuangketkeow as a Deputy stated that Thailand has believed in addressing issues through dialogue. Cambodia has approached the issues differently. It always claims that it respects international law and portrays Thailand as flouting it, but its claims are self-serving and contain elements of hypocrisy. 

“When Cambodia leaked a private telephone conversation between our leaders, when Cambodian rockets hit and killed innocent Thai civilians, and when our soldiers lost their legs to landmines planted by Cambodia, where was respect for international law?” said Sihasak.

Thailand viewed international law and diplomacy as complementary foundations of peaceful relations between states. The country repeatedly sought resolutions to restore relations. 

Instead of engaging fully and sincerely through bilateral dialogue, Cambodia has repeatedly vilified Thailand through false narratives, distortion of facts and unfounded accusations on an almost daily basis, including at international forums. “And it does this by playing the role of a victim with a sense of self-righteousness aimed at claiming the moral high ground,” said the Thai Foreign Minister.

Regarding the termination of the 2001 MOU, Cambodia’s claim that Thailand’s decision left it with no option but to initiate these proceedings, is simply not true. 

Over a period of 25 years, both counties managed to hold only two rounds of official talks. It is clear that the MOU had produced no concrete progress. Thailand therefore chose to make a fresh start in negotiations. 

Thailand also believes that Cambodia’s recent ratification of UNCLOS would have provided a timely opportunity to resume talks. Thailand proposed direct talks on the maritime boundary, but Cambodia disregarded the option. 

Sihasak asserted that the scope of these proceedings concerns only delimitation of the maritime boundary between Thailand and Cambodia in the Gulf of Thailand. It does not concern sovereignty over land, including Koh Kut. There has never been a debate on this matter. Thailand also rejects Cambodia’s 1972 continental shelf claim line which is without legal basis.

Thailand and Cambodia have disputed maritime boundaries for decades, leading them to enter into the 2001 MOU to delimit the boundary and share the natural resources. Playing along with nationalist sentiment, PM Anutin Charnvirakul vowed to cancel the MOU and kept his word by announcing the termination of the 2001 MOU, citing that it had made no progress. 

On 2 June, Cambodia initiated the compulsory conciliation process under UNCLOS, which either party is allowed to invoke without consent from the other party. Compulsory conciliation has previously been invoked only once, in the dispute between Timor-Leste and Australia over the Timor Sea.

Thailand later submitted a response agreeing to enter the proceedings, making this only the second case in the history of the international law of the sea. Each country appointed two conciliators, and these four selected a chair to form the Commission.

Thailand named Judge Albert J. Hoffmann of South Africa and Judge Rüdiger Wolfrum of Germany. Cambodia named French academic Jean-Marc Thouvenin and Danish diplomat Peter Taksøe-Jensen. Australian diplomat Katrina Cooper was then appointed as the Chair 

What do their statements reveal?

Given that compulsory conciliation proceedings typically aim at finding common ground for both parties to resolve an issue, several observers expressed concerns over Thailand’s assertive tone, as the proceedings rely on trust from both sides.

Ultimately, both Thailand and Cambodia, under the UNCLOS mechanism, will inevitably have to find an amicable solution.

The standpoints of both Thailand and Cambodia are also interesting. Cambodia laid out two options: ‘a single all-purpose maritime boundary,’ or ‘an agreement on the joint development and equitable sharing of resources, pending final agreement on a maritime boundary’.

The inclusion of joint development also suggests that Cambodia continues to favour the model it has prioritised for the disputed maritime areas.

Joint development is part of a provisional arrangement under UNCLOS in which disputing countries agree to share the natural resources pending final maritime delimitation. However, it is not mandatory. 

In the Gulf of Thailand, we have seen one example of joint development: between Thailand and Malaysia. 

Also, the term ‘equitable’ in Cambodia’s statement does not appear to be random. In the context of UNCLOS, this does not always mean a 50:50 split of resources in the disputed area. Maritime delimitation considers a range of factors, including geography, coastline, historical circumstances, economic considerations, and, in some cases, environmental concerns.

Meanwhile, Thailand proposes only one solution: 'maritime boundary delimitation between Thailand and Cambodia,’ which was also its longstanding position before the negotiations to enter into the 2001 MOU. 

Phattharaphong Saengkrai of Thammasat University's Faculty of Law observes that given the proceedings take approximately 12 months, it would be impossible to achieve a single all-purpose maritime boundary to cover the 26,000 sq km. overlapping area as Cambodia proposes.

In addition, he noted that Sihasak’s statement indicates that Thailand does not want to be seen as allowing an external party to influence its decision-making. Although the Commission’s recommendations are not legally binding, they carry political and diplomatic weight.

At the very least, in Phattaraphong’s assessment, Thailand and Cambodia are likely to negotiate a new detailed MOU that sets out a framework for further negotiations, while the two sides might agree on boundary lines in certain disputed areas. 

Koh Kut is also the most controversial part in the dispute. Cambodia’s claimed line forms a U shape curve around Thailand’s Koh Kut. But Under UNCLOS, an inhabited island is entitled to its own territorial sea, EEZ and continental shelf. Thailand, therefore, argues that Cambodia must redraw its line in a straight southwesterly direction away from the island. Thailand is likely to be in a strong legal position at this point.

Whether their proposed options can be reconciled will depend on the extent to which both parties agree. It is to be noted that the Commission is not responsible for drawing the line for both parties, and there will be no winner or loser from the compulsory conciliation.