Can Compulsory Conciliation Resolve the Cambodia-Thailand Maritime Border Dispute?

Compulsory conciliation under UNCLOS can force Cambodia and Thailand into a structured process, but it cannot impose a maritime boundary on either of them. Cambodia launched the proceedings on 2 June 2026, after Thailand terminated the 2001 memorandum of understanding that had governed talks for a quarter of a century. A conciliation commission must report within twelve months of being constituted, and that report is not binding.

Its real value is a neutral, documented baseline for a dispute that has stalled for decades.

What is actually in dispute in the Gulf of Thailand

The disagreement covers an overlapping claims area of roughly 26,000 square kilometers (about 10,000 square miles) in the Gulf of Thailand. Both states drew continental shelf claims in the 1970s using different baselines and different treatment of the island of Koh Kut, which produced claim lines that cross.

The commercial stake is energy. Industry estimates put the area's resources near 12 trillion cubic feet of natural gas along with oil, with headline valuations around 300 billion US dollars. None of it has been developed. No operator commits a drilling campaign to contested acreage without a title that lenders and underwriters will accept.

How compulsory conciliation works under UNCLOS

Part XV of UNCLOS sets out dispute settlement. Article 298 lets a state exclude sea boundary delimitation from binding arbitration or adjudication, and both Cambodia and Thailand have filed declarations of that kind.

The trade-off sits in Annex V, Section 2. A state that opts out of binding settlement for delimitation still accepts compulsory conciliation, which the other party may start unilaterally once negotiation has failed. The mechanics are specific:

• A commission of five conciliators is constituted, with each party appointing two and the four selecting a chair.
• The commission hears both parties and may propose terms of settlement.
• It must report within twelve months of being formed.
• The report and its recommendations do not bind either government.

Cambodia could only reach for this mechanism recently. It signed UNCLOS in 1983 but did not ratify until 16 January 2026, and ratification was the precondition for filing.

The single precedent: Timor-Leste and Australia

Compulsory conciliation has been used once before, in the Timor Sea dispute between Timor-Leste and Australia across 2016 and 2017. It worked. Australia challenged the commission's competence at the outset, lost that argument, and the two states signed a maritime boundary treaty in 2018.

The lesson is that non-binding does not mean powerless. A commission puts a neutral record on the table and attaches a deadline to it, which shifts the domestic politics of compromise on both sides.

Where the two governments disagree about the process itself

Phnom Penh and Bangkok do not agree on what the conciliation should cover. Cambodia wants the boundary and a joint development framework for offshore energy handled together. Thailand argues the immediate task is delimitation of the boundary and continental shelf alone.

That is not a technicality. Joint development arrangements let states share revenue while leaving sovereignty unresolved, which is how Malaysia and Thailand handled their own overlapping area. Settling the scope therefore decides whether a commercial outcome is available without a full boundary settlement first.

Why shipping and offshore operators should follow this

The Gulf of Thailand is working water. It carries feeder traffic to Sihanoukville, Laem Chabang and Map Ta Phut, large fishing fleets, and producing offshore infrastructure on both sides of the contested block.

Three operational consequences follow from an unresolved line:

• Survey and drilling exposure. Seismic vessels and mobile drilling units working near a contested boundary attract naval and coast guard attention, and charter parties for that work carry specific exclusions.
• Enforcement uncertainty. Fishing vessel detentions and boarding disputes cluster around unsettled lines, and crews of any nationality can be caught up in them.
• Insurance and finance. Underwriters and lenders price contested acreage differently, which is the practical reason the area has stayed undrilled.

The land border between the two states has also seen armed clashes in recent years, which raises the cost of any escalation at sea. A conciliation report will not redraw a chart on its own. It will tell operators whether a negotiated development framework is realistic within the next few years, and that is the answer worth watching for.

Sources and further reading

• Can 'Compulsory Conciliation' Resolve the Cambodia-Thailand Maritime Border Dispute? (The Diplomat)
• Cambodia initiates UN mediation over Thailand maritime boundary dispute (JURIST)
• Revisiting the Cambodia-Thailand Maritime Dispute (East-West Center)
• Thailand and Cambodia diverge over UNCLOS maritime talks and Gulf energy resources (The Nation Thailand)

What to read next

• Maritime Engineer Role Overview
• Largest Ships in Maritime History
• Saudi Arabia Launches Maritime Coalition to Strengthen Security in the Red Sea