Thailand Tore Up a 25-Year Pact With Cambodia. Now a $300 Billion Energy Dispute Heads to the UN.

A border dispute that the two countries spent a quarter-century agreeing to talk about has become a dispute they will now argue out in front of the United Nations.

On June 2, Cambodian Prime Minister Hun Manet announced that Cambodia had sent a formal notice to Thailand and to the U.N. secretary-general to begin compulsory conciliation proceedings under the United Nations Convention on the Law of the Sea, or UNCLOS. The move was Phnom Penh’s answer to a decision in Bangkok weeks earlier: on May 5, the Thai cabinet voted to unilaterally withdraw from a 2001 agreement that had served, however imperfectly, as the framework for managing the countries’ overlapping claims in the Gulf of Thailand.

The stakes are not abstract. The contested zone covers roughly 26,000 square kilometers of the Gulf, an area Thailand’s own energy ministry has valued at around $300 billion in undersea oil and gas. For two decades, that prize sat behind a diplomatic stalemate. Now it sits inside a legal process neither government fully controls — and along a Southeast Asian fault line that both Washington and Beijing have reasons to watch.

What Happened

The agreement Thailand scrapped is known as “MoU 44,” a reference to the Buddhist calendar year 2544, when it was signed in 2001. It did not resolve the maritime boundary; it established a structure for negotiating both the boundary demarcation and the possibility of jointly developing the oil and gas beneath the overlapping claims. In practice, it produced more meetings than progress.

Cancelling it was a campaign promise. Thai Prime Minister Anutin Charnvirakul had pledged during the run-up to Thailand’s February 8 election to tear up MoU 44, casting the long-stalled pact as a concession that had delivered nothing. After taking office, he made good on it. Anutin said his government revoked the memorandum because of the long-standing failure to implement it.

Cambodia’s response was to escalate, not retreat. Rather than accept the loss of the negotiating framework, Phnom Penh invoked UNCLOS, the international treaty that governs maritime rights and includes mechanisms for forcing disputes into third-party review. Compulsory conciliation, the route Cambodia chose, is rare — it convenes a panel of independent experts to examine a dispute and recommend a settlement. Its recommendations are not legally binding on either side, but the process itself is difficult to refuse and puts the disagreement under international scrutiny.

The Timeline

The maritime fight did not arrive in isolation. It followed a sharp deterioration in relations along the countries’ land border, where two rounds of deadly clashes hardened public opinion in both capitals and pushed nationalism to the front of the politics on each side.

The sequence is compressed. The Thai cabinet voted to withdraw from MoU 44 on May 5. On June 2, Hun Manet announced Cambodia’s letter to Thailand and the U.N. secretary-general initiating compulsory conciliation. Three days later, on June 5, Thailand said it would participate in the UNCLOS process Cambodia had chosen — but Anutin paired that acceptance with a hard line on everything else. “We will use UNCLOS, which means from now on there will be no more talks…or other forms of cooperation,” he said, signaling that Bangkok would freeze the broader bilateral channels, including those meant to manage the land border, and route the maritime question exclusively through the U.N. mechanism.

Under the conciliation procedure, Thailand now has 21 days to appoint two conciliators of its own. Those appointees then join Cambodia’s in jointly selecting a chair for the commission, with the whole process overseen by the U.N. secretary-general. It is a slow machine, designed to lower the temperature rather than deliver a quick verdict.

The choice of forum is itself a strategy. By invoking UNCLOS rather than waiting for Thailand to return to the table, Cambodia locked the dispute into an international track that Bangkok cannot quietly abandon and that carries the implicit weight of global legal norms. It is also a notable use of an obscure mechanism: compulsory conciliation has been invoked only a handful of times in the history of the convention, most prominently in a maritime case between Timor-Leste and Australia that produced a negotiated boundary. Phnom Penh is betting that the same machinery can pry open a question that two governments, left to themselves, kept frozen for a generation.

The U.S. Angle

For American readers, the dispute is easy to file under distant regional friction. It is more than that, because of where it sits and who else has a stake in the answer.

Thailand is the oldest U.S. treaty ally in Asia and a designated major non-NATO ally, a relationship that gives Washington a direct interest in Thai stability and in keeping a long-standing partner from being drawn deeper into confrontation. Cambodia, meanwhile, has moved steadily closer to China. Beijing struck a 2019 arrangement to help develop and use the Ream Naval Base on Cambodia’s coast, and has supplied the country with military hardware and funding — ties that have repeatedly worried U.S. officials about China’s growing footprint on the Gulf.

That backdrop turns a bilateral energy quarrel into something the broader U.S.-China contest runs through. The Gulf of Thailand is woven into the wider Indo-Pacific competition that has defined regional diplomacy, the same rivalry visible in the high-stakes summitry between Washington and Beijing over trade and security. A maritime fault line that splits a U.S. ally from a Chinese partner is precisely the kind of seam outside powers can be tempted to widen.

There is an energy dimension, too. The disputed block’s value lies in oil and gas that has stayed in the ground for two decades because no one could agree on who owns it. Conciliation will not change that overnight, but any path toward developing those reserves — or any new freeze on them — feeds into the global supply picture at a moment when energy markets are already strained, a tension running through everything from Middle East supply shocks to the realignments reshaping the world’s major oil producers.

What Comes Next

The immediate clock is the 21-day window for Thailand to name its conciliators, a step Bangkok has signaled it will take rather than boycott. After that, the commission forms and begins what is likely to be a months-long examination of competing claims that have resisted resolution since the agreement was first signed in 2001.

What conciliation cannot do is force a binding outcome. Its recommendations will carry the weight of an independent international panel and the oversight of the U.N. secretary-general, but neither government is obligated to accept them. That leaves the real test further out: whether a non-binding process can produce enough common ground to reopen talks the two sides have just shut down, or whether the $300 billion question simply moves from a stalled negotiating table to a slow-moving U.N. file.

For now, the two neighbors have agreed on exactly one thing — to disagree somewhere new. After 25 years of managing the dispute between themselves, Thailand and Cambodia have handed it to the United Nations, and to a process whose chief virtue is that it is hard for either of them to walk away from.