The long-standing border dispute between Thailand and Cambodia has resurfaced in public debate following Prime Minister Anutin Charnvirakul’s announcement that his government plans to hold a national referendum, likely alongside the next election, to ask voters whether Thailand should revoke or retain two key bilateral agreements — MoU 43 (on land boundaries) and MOU 44 (on overlapping maritime zones).
The move revives one of the most sensitive issues in Thai national security policy — how to manage complex, overlapping territorial claims with Cambodia that have periodically triggered military clashes and fueled nationalist tensions for more than two decades.
What is MOU 43?
MoU 43 — officially the Memorandum of Understanding between Thailand and Cambodia on the Survey and Demarcation of [the] Land Boundary — was signed on June 14, 2000, during the government of then-prime minister Chuan Leekpai.
Its purpose was not to redefine borders but to establish a framework and mechanism for jointly surveying and demarcating the land boundary, which stretches nearly 800 kilometres — a process which remains unfinished to this day.
Background
After Cambodia’s internal conflict ended in the mid-1990s, Bangkok and Phnom Penh resumed talks to clarify poorly defined border segments rooted in colonial-era treaties between Siam and France, which then ruled Indochina. The treaties of 1904 and 1907, along with their associated maps, left ambiguous demarcations — particularly around the Preah Vihear Temple and adjoining highlands — creating “overlapping areas”.
Why it was needed
Before MoU 43, the two countries faced recurring disputes over several unresolved issues. Chief among them was the interpretation of Franco-Siamese treaties and maps, particularly the Dangrek map, which Thailand never formally endorsed and claims was inaccurately drawn, placing Preah Vihear on the Cambodian side.
Tensions were also rooted in the 1962 International Court of Justice ruling, which awarded the temple itself to Cambodia but left the surrounding land undefined, creating a 4.6-square-kilometre overlapping zone. In addition, large sections of the 800-kilometre border remained undemarcated after the Cold War, while villagers, loggers, and military patrols frequently clashed along disputed stretches, sometimes escalating into armed skirmishes.
Key provisions of MOU 43
Under MoU 43, both sides agreed not to unilaterally alter the border landscape, such as by constructing buildings or digging trenches. The agreement also established a Joint Boundary Commission (JBC) to conduct surveys, install boundary markers, and resolve disputes through dialogue.
What is MOU 44?
MoU 44 — the Memorandum of Understanding between the Government of the Kingdom of Thailand and the Government of the Kingdom of Cambodia Concerning the Area of Their Overlapping Maritime Claims to the Continental Shelf — was signed on June 18, 2001, under the government of Thaksin Shinawatra.
It addresses the Overlapping Claims Area (OCA) in the Gulf of Thailand, covering about 26,000 square kilometres, where both countries have laid claim to the continental shelf since the 1970s.
Why it was signed
Both nations declared their respective continental shelves in 1972-1973, but the boundaries overlapped significantly. The area was later found to contain abundant petroleum and natural gas reserves, making cooperation not only economically desirable but also politically sensitive.
Core principles
MoU 44 established two main frameworks. First, both countries agreed to negotiate an arrangement for joint petroleum exploration and production within a designated Joint Development Area (JDA), with the aim of sharing economic benefits from natural resources. Second, the two sides committed to continuing talks to establish a permanent maritime boundary. The Overlapping Claims Area (OCA) in the Gulf of Thailand, jointly claimed by Thailand and Cambodia, spans approximately 26,000 square kilometres.
Most crucially, Article 5 of the MoU stipulates that until delimitation is completed, neither party’s signature affects its legal claim — meaning no sovereignty was surrendered by either side. In essence, MoU 44 created a framework for future negotiation, rather than a binding concession of territory or rights.
Calls to cancel MOU 43-44
The movement to revoke both MoUs resurged after deadly clashes along the Thai-Cambodian border on July 24, 2025, which left soldiers and civilians dead on both sides, particularly near Ta Muen Thom Temple and Chong Arn Ma Pass. Although a ceasefire was reached on July 28, the political fallout remains intense.
Conservative factions — including senators, members of the Palang Pracharath Party and the Bhumjaithai Party (then in opposition) — together with nationalist groups led by Sondhi Limthongkul, accused the previous Pheu Thai government under Paetongtarn Shinawatra of jeopardising national interests.
They alleged that Thaksin Shinawatra’s close ties with former Cambodian leader Hun Sen had influenced bilateral talks, prioritising personal or business interests over national sovereignty, particularly in relation to the maritime energy resources covered under MoU 44. Opponents further claim the Thaksin and Hun Sen families could benefit from joint petroleum ventures in the overlapping maritime zone, potentially at Thailand’s expense.
Critics also argue that MoU 43 has failed to prevent repeated incursions by Cambodian troops and civilians, despite hundreds of alleged violations, including the construction of structures, trench-digging, and land-use changes in disputed areas.
According to the Royal Thai Armed Forces, there have been 400-500 similar instances of illegal crossings by both the military and civilians from the other nation since 2000.
Meanwhile Cambodian authorities have countered with accusations of more than 695 similar Thai breaches in the opposite direction– underscoring the deep mutual distrust.
The map controversy
A technical but crucial issue lies in the choice of maps used for border demarcation. Cambodia favours the 1:200,000 scale French colonial map (1905-1908), arguing that it carries historical legitimacy. Thailand, however, insists on the 1:50,000 scale map, which more accurately reflects natural watershed lines and provides greater topographical precision. Thai experts argue that reliance on the French map would reduce Thai territory, particularly around the Dangrek Mountains and the Preah Vihear area.
The current situation
While nationalist rhetoric is on the rise, many experts caution against any unilateral withdrawal from MoUs 43 and 44. Scholars and diplomats warn that revoking either agreement without Cambodia’s consent and without an alternative legal framework could leave Thailand without a dispute-management mechanism, heightening the risk of renewed clashes.
Such a move could also be viewed internationally as a treaty violation, undermining Thailand’s credibility, and might even expose the country to another case at the International Court of Justice (ICJ), with Cambodia potentially reviving unresolved complaints — much like the 1962 Preah Vihear ruling, in which Thailand lost.
Parliament and Senate have established special committees to examine the advantages and drawbacks of termination, though their findings are still pending.
The referendum debate
Mr Anutin’s proposed referendum has sparked sharply divided opinions.
Supporters view it as a democratic solution that gives citizens a direct voice on sovereignty issues. Opponents counter that border and maritime treaties are highly technical matters requiring expert negotiation and legal precision, not populist voting.
Critics have also accused the ruling Bhumjaithai Party of using the referendum as a nationalist campaign tool ahead of the next election — a strategy to project patriotism and consolidate its political base among conservative voters.
What lies ahead?
If the referendum proceeds, it could reshape both Thailand’s regional diplomacy and its domestic politics. Revoking the agreements could reignite tensions with Cambodia and complicate Asean cooperation, while retaining them might anger nationalist voters but preserve stability and international credibility.
Either way, the fate of MoUs 43 and 44 highlights Thailand’s enduring dilemma: how to balance national pride, regional peace, and pragmatic diplomacy in one of Southeast Asia’s most sensitive border disputes.