Maritime dispute: Cambodia faces Thailand before the UN conciliation commission

H.E. Prak Sokhonn led the Cambodian delegation and legal team into Singapore on Sunday morning. The first meeting of the conciliation commission constituted under Annex V of the UN Convention on the Law of the Sea runs from 14 to 16 September. Part of the Kingdom’s energy future is at stake, four months after Bangkok tore up the only bilateral framework the two countries had.

Two ministers and a legal team

Deputy Prime Minister and Minister of Foreign Affairs and International Cooperation Prak Sokhonn sits as Cambodia’s Agent. Lam Chea, Minister in Charge of the State Secretariat of Border Affairs, is Deputy Agent. Both are accompanied by a delegation and a legal team.

On the Thai side, Foreign Minister Sihasak Phuangketkeow acts as Agent and Ambassador Songchai Chaipatiyut as Deputy Agent. Bangkok has announced the attendance of specialists from the Hydrographic Department and the Naval Operations Department of the Royal Thai Navy, as well as from the Department of Mineral Fuels under the Ministry of Energy. The line-up says a good deal about what is at stake.

Opening statements by both parties are scheduled for 15 September at 8 a.m. Cambodia time, 9 a.m. in Singapore. They will be open to the public and webcast live in Khmer, English and Thai. Prak Sokhonn will deliver Cambodia’s.

A conciliation, not a trial

The proceedings are not an arbitration. Compulsory conciliation under Annex V of UNCLOS is a non-adjudicatory mechanism: a neutral commission helps the parties identify common ground and seek an amicable settlement. It hands down no judgment and does not itself draw the maritime boundary.

At the end of its work, the commission issues a report with recommendations. These do not bind the states. Their weight is diplomatic and technical: they give governments outside cover for concessions that would be politically costly to make alone.

The commission has five members. Cambodia appointed Danish ambassador Peter Taksøe-Jensen and French professor of international law Jean-Marc Thouvenin. Thailand named two former presidents of the International Tribunal for the Law of the Sea, Germany’s Rüdiger Wolfrum and South Africa’s Albert Hoffmann. The four conciliators then chose Australian diplomat and lawyer Katrina Cooper as chairperson. The Permanent Court of Arbitration acts as registry, under case number 2026-35.

Why conciliation rather than a court

The choice of mechanism follows a precise legal logic. Article 298 of UNCLOS allows a state to exclude maritime delimitation disputes from the compulsory procedures that lead to a binding decision. Thailand, which ratified the convention in 2011, filed such a declaration. Cambodia did the same on accession.

The consequence is that neither the International Court of Justice, nor the International Tribunal for the Law of the Sea, nor an Annex VII arbitral tribunal can be seised unilaterally. What remains is compulsory conciliation, which a state filing that declaration is obliged to accept. It was the only door Phnom Penh could open without Bangkok’s agreement.

Cambodia made sure its own paperwork was in order first. A signatory to the convention since 1 July 1983, it had never ratified it. The National Assembly did so on 16 January 2026 by 114 votes to nil. The instrument was deposited on 6 February and the convention entered into force for the Kingdom on 8 March, making it the 172nd State Party.

A 26,000 sq km area disputed since 1972

The substance of the case goes back half a century. In 1972 Cambodia published the delimitation of its continental shelf in the Gulf of Thailand. Thailand did the same the following year, along an incompatible line. The two claims cross around the Thai island of Koh Kut and carve out an overlapping claims area estimated at 26,000 to 27,000 square kilometres.

That marine quadrilateral is not a cartographic abstraction. Available estimates put some 1.6 billion barrels of oil and 17 trillion cubic feet of natural gas beneath it. No drilling has ever been authorised there, for want of agreement on the status of the waters.

The memorandum of understanding signed in 2001, known in Thailand as MoU 44, set out the principle of parallel negotiations on delimitation and on joint development of the resources. It served as the sole framework for twenty-five years. It produced nothing tangible.

May 2026: Bangkok walks out

On 5 May 2026, the Thai cabinet under Anutin Charnvirakul approved the unilateral cancellation of the 2001 memorandum. Bangkok presented the move as an adjustment of the cooperation framework rather than a break in relations, saying it intended to continue talks using UNCLOS as the common reference.

Phnom Penh responded within a month. On 2 June, Hun Manet announced that notification had been sent to Thailand and to the UN Secretary-General to initiate compulsory conciliation. Both chambers of parliament endorsed the step. The Prime Minister stressed one point: this is not an escalation but a negotiation facilitated by international experts.

Thailand replied on 19 June, formally agreeing to take part while restating two reservations. The process is not a court case and its outcome will not be legally binding. More importantly, Bangkok holds that its scope should be limited to maritime delimitation.

The real disagreement is about scope

That is where the immediate fault line lies. Cambodia’s notification covers not only delimitation but also provisional arrangements for joint development and equitable resource sharing. Thailand wants the commission confined to drawing the boundary.

The difference is not rhetorical. A conciliation limited to the boundary can run for years without unlocking a single gas field. A conciliation extended to provisional arrangements can produce a working agreement before the boundary is ever fixed. It is one of the first questions the commission will have to settle in Singapore.

The Timor-Leste–Australia precedent

Phnom Penh readily cites a precedent. In April 2016 Timor-Leste triggered the first ever compulsory conciliation under Annex V, against Australia, in the Timor Sea. Canberra challenged the commission’s competence; the commission found in September 2016 that it was competent.

The process ran for two years, with sessions in The Hague, Singapore and Kuala Lumpur. It led to the signature, on 6 March 2018 at UN headquarters in New York, of a treaty establishing the maritime boundary between the two countries, alongside a special regime for the Greater Sunrise gas field. The commission issued its final report two months later.

The parallel has limits. The Timor case set a small state against a distant partner, with no shared land border and no recent armed conflict. That is not the situation here.

A negotiated sea, a closed land border

The proceedings unfold against a land-border rupture. Fighting along the frontier in July 2025, then again in December, left more than a hundred dead and displaced several hundred thousand people on both sides. A ceasefire was signed on 27 December 2025.

Land crossings have been shut since June 2025. Cross-border road services are suspended, tens of thousands of Cambodian migrant workers have returned home, and Cambodian tourism recorded a 46% fall in international arrivals over the first seven months of 2026. Only air links are operating.

The maritime conciliation is legally separate from the land dispute. Politically, it feeds on it.

Three days in Singapore

This week’s meeting is primarily procedural. It will set the calendar, the working methods and the scope of the proceedings. The opening statements on 15 September will be public; what follows will be held under the confidentiality regime usual in such cases.

In its statement, Cambodia’s Ministry of Foreign Affairs restated its position of principle: international law provides the foundation for the peaceful settlement of disputes between states. Cambodia, the text says, enters the proceedings in good faith and in a spirit of cooperation, with full confidence in the commission.

The commission itself has no power of compulsion. Its influence will depend on what the two delegations are willing to put on the table from Monday.