Thailand’s decision to terminate the 2001 Memorandum of Understanding (MOU) with Cambodia on maritime claims in the Gulf of Thailand may satisfy long-standing domestic political demands, but the harder challenge lies ahead. The legal, diplomatic, and political consequences that follow could prove significantly more complex than the act of cancellation itself.

The Thai cabinet’s resolution on May 5 to end the 2001 MOU marked a major turning point in bilateral relations over overlapping maritime claims. Signed during the administration of former Prime Minister Thaksin Shinawatra, the agreement sought to create a framework for addressing disputes over approximately 26,000 square kilometres of overlapping continental shelf claims in the Gulf of Thailand.

Importantly, the MOU was not merely a technical arrangement for maritime boundary discussions. It was designed as a comprehensive and inseparable package that combined two politically sensitive objectives: the delimitation of maritime boundaries and the joint development of hydrocarbon resources in disputed areas. In practice, this meant that sovereignty-related questions and energy cooperation were to be addressed simultaneously rather than separately.

Over the past two decades, however, negotiations under the MOU made little meaningful progress. Critics in Thailand increasingly viewed the arrangement as diplomatically ineffective and politically costly, particularly amid concerns surrounding Koh Kut in Trat province and fears that joint resource development could undermine territorial claims.

Prime Minister Anutin Charnvirakul’s government therefore framed the termination as a necessary reset. Speaking after meeting Cambodian Prime Minister Hun Manet on the sidelines of the ASEAN Summit in the Philippines, Anutin stated that Cambodia had already been informed of Thailand’s decision and acknowledged it officially.

Yet the legal process surrounding the termination remains less straightforward than the political narrative suggests.

Questions have emerged regarding whether the termination should have followed formal procedures under the 1969 Vienna Convention on the Law of Treaties, which generally requires written diplomatic notification and procedural clarity in treaty withdrawal. Some legal observers have also questioned whether parliamentary or Constitutional Court involvement may have been necessary, given the implications for international commitments.

The Thai government, however, appears to interpret the matter differently, emphasizing political communication between leaders and the practical reality that Phnom Penh has already been informed.

Regardless of procedural debates, the more significant question is what follows after the MOU.

Thailand’s foreign ministry has signaled that ending the agreement does not mean abandoning peaceful dispute settlement. Deputy Prime Minister and Foreign Minister Sihasak Phuangketkeow has reiterated Bangkok’s preference for continued negotiations under the framework of the 1982 United Nations Convention on the Law of the Sea (UNCLOS), which both Thailand and Cambodia have ratified.

From Bangkok’s perspective, the recent ratification of UNCLOS-related mechanisms by Cambodia and the lack of meaningful progress under the MOU may justify resetting negotiations under a more contemporary legal framework.

Phnom Penh, however, appears to view the post-MOU landscape differently.

Cambodian Prime Minister Hun Manet has described the 2001 MOU as the only mutually accepted bilateral mechanism for peaceful maritime dispute management and expressed regret over Thailand’s unilateral withdrawal. Cambodia has signaled that it may pursue compulsory conciliation under UNCLOS, arguing that international legal mechanisms now represent the most appropriate avenue for resolving the issue.

This distinction matters because compulsory conciliation under Annex V of UNCLOS differs substantially from ordinary bilateral negotiations.

Unlike arbitration or adjudication, compulsory conciliation is a non-binding process in which an independent commission examines the dispute, hears arguments from both sides, and offers recommendations. Although the recommendations themselves are not legally enforceable, the process may carry considerable diplomatic and political weight, particularly when one side seeks international legitimacy for its position.

Cambodia’s position rests partly on Article 12 of Annex V, which states that a party’s refusal to participate does not prevent proceedings from continuing. This provision has attracted increased attention following the 2016–2018 compulsory conciliation between Timor-Leste and Australia, often cited as a landmark case in maritime dispute settlement.

In that case, the conciliation commission clarified that Article 298 of UNCLOS—which requires that negotiations fail within a reasonable period before compulsory conciliation proceeds—does not grant either party an effective veto simply by refusing to negotiate. For some Cambodian observers, this precedent suggests Phnom Penh could proceed with international mechanisms even if Thailand remains hesitant.

Thailand, however, has not yet clearly indicated whether it would accept such a path. Foreign Minister Sihasak has denied reports that Bangkok has already agreed to compulsory conciliation, emphasizing that multiple diplomatic steps remain before any formal process begins.

This legal ambiguity has increasingly spilled into the political sphere. Former Cambodian Prime Minister Hun Sen publicly criticised Thailand’s position, arguing that Bangkok’s unilateral cancellation of the MOU had already dismantled the bilateral framework for negotiations, thereby strengthening the rationale for proceeding directly under UNCLOS mechanisms.

The risk, therefore, is that what began as an attempt to reset negotiations may instead evolve into a diplomatic disagreement over process itself.

At the same time, neither Thailand nor Cambodia can afford to ignore the practical realities behind the dispute. Studies estimate that the overlapping maritime area may contain around 11 trillion cubic feet of natural gas and between 300–500 million barrels of crude oil, with a combined economic value reaching approximately US$300 billion. These resources could become increasingly important as both countries face rising energy insecurity amid instability in the Middle East and volatile global energy markets.

For both governments, the challenge ahead is not simply who wins the legal argument, but whether they can avoid allowing maritime disputes to undermine longer-term economic and energy interests. Terminating the MOU may have been politically achievable. Managing what comes next under UNCLOS may prove considerably harder.