ASEAN Beat | Diplomacy | Southeast Asia

Escaping the Escalation Trap in the Thailand-Cambodia Maritime Dispute

Compulsory conciliation under UNCLOS could help both sides insulate sensitive negotiations from domestic political pressure.

A detail of a British admiralty chart of the Gulf of Thailand published in 1957, which shows the island of Koh Kut.

The Gulf of Thailand forms the second axis of the Cambodia-Thai border dispute. The 27,000-square-kilometer Overlapping Claims Area has been disputed since 1972 and is estimated to hold some 1.6 billion barrels of oil and 17 trillion cubic feet of natural gas. Thailand terminated the 2001 memorandum of understanding governing talks over the OCA in early 2026, after fighting along the two nations’ disputed land border in July and December 2025. The outbreak of war reignited historic territorial and political animosities between the two Southeast Asian states and resulted in a border closure that still persists.

The immediate cause of the fighting was a calculated political leak by Cambodian Senate President Hun Sen of a private 17-minute telephone conversation with Thai Prime Minister Paetongtarn Shinawatra. The recording exposed Paetongtarn adopting a deferential posture toward Phnom Penh while offering critical remarks regarding her own military commanders.

As Hun Sen no doubt intended, the political fallout in Bangkok was swift. The leak locked Thai political elites into a severe audience cost escalation trap, where public outrage severely restricted their diplomatic flexibility. Paetongtarn’s political credibility evaporated almost overnight, and a wave of hyper-nationalism culminated in her suspension and removal from office by the Constitutional Court. Domestic political discourse in Thailand became thoroughly militarized, effectively ending any immediate possibility of bilateral compromise with Cambodia.

Riding this surge of populist anger, Anutin Charnvirakul and his Bhumjaithai Party secured victory in the February 2026 election. Anutin formed a hardline government that explicitly prioritized security, deferring border management directly to military commanders. Fulfilling a key electoral pledge to his nationalist base, Anutin’s cabinet formally approved the unilateral termination of the 2001 MoU. For nearly 25 years, the agreement had provided the only framework for maritime boundary delimitation and joint energy development between the two neighbors.

To justify scrapping the agreement without a formal exit clause, Thai legal strategists invoked Article 56 of the 1969 Vienna Convention on the Law of Treaties, claiming an implicit right of denunciation based on Cambodia’s alleged failure to engage in negotiations. But the move was motivated above all by domestic politics: it was intended to project strength and to signal to voters that the legacy of former Prime Minister Thaksin Shinawatra, under whose administration the 2001 MoU was originally drafted, was officially over. However, by dismantling the agreement, Bangkok simultaneously destroyed the remaining institutional safeguards governing the maritime boundary.

Phnom Penh responded immediately to Thailand’s unilateral exit. Condemning the move as a breach of international legal obligations, the Cambodian government announced it would initiate compulsory conciliation under Annex V of the United Nations Convention on the Law of the Sea (UNCLOS). It was a shrewd political move. Having suffered a military defeat on the land border and remaining in an inferior position to its Thai counterpart, Cambodia was also facing increasing pressure from powerful states due to its domiciling the online scamming industry. Hun Manet engaged in forum shopping, choosing a legal avenue that promised low cost and high potential reward. By choosing compulsory conciliation, Cambodia has demonstrated its resolve to be a “good member” of the international community, pull Thailand into a non-binding, low-sovereignty-cost legal mechanism, and demonstrate to the Cambodian people a willingness to “stand up” to a superior........

© The Diplomat