Thailand and Cambodia lock horns over Gulf of Thailand boundary in UNCLOS talks
The first formal session of a UN-backed conciliation commission on Thailand and Cambodia’s maritime dispute took place in Singapore from September 14–16, 2026, with both sides refusing to budge on core demands. While Cambodia seeks immediate cooperation on shared resources, Thailand insists the boundary itself must be settled first — a position that could delay any economic progress in the disputed zone for months.
The conciliation process is set to last 11–12 months. Neither side is legally obligated to accept the commission’s final recommendations, making the outcome advisory at best.
What’s at stake in the Gulf
The conflict centers on an overlapping claim area of 26,000–29,000 square kilometers in the Gulf of Thailand, a region suspected to hold oil and natural gas deposits worth up to $300 billion. The dispute stems from conflicting boundary lines drawn by each country in the early 1970s, based on old colonial-era surveys. Cambodia, which finally ratified UNCLOS in February 2026 as the last ASEAN nation to do so, triggered compulsory conciliation in June after Thailand scrapped a 2001 memorandum of understanding on overlapping claims.
Thailand’s Deputy Prime Minister and Foreign Minister, Sihasak Phuangketkeow, made it clear at the Singapore meeting that Bangkok’s sole goal is to define the maritime border. He rejected any attempt to merge negotiations over resource sharing or joint exploration into the current process, stating: “The Commission’s mandate is to delimit the boundary — nothing else.”
Cambodia’s delegation, led by Deputy Prime Minister and Foreign Minister Prak Sokhonn, countered that a single boundary is meaningless without rules for resource access. Phnom Penh has proposed two paths: either a binding treaty on the entire maritime border, or a provisional deal allowing shared development of hydrocarbon reserves while final delimitation is worked out.
Why Koh Kood matters — and why it doesn’t
Thailand has repeatedly stressed that the conciliation process does not cover land sovereignty, particularly concerning Ko Kut (Koh Kood), a small island on its eastern coast near Cambodia’s Koh Kong province. Cambodia’s 1972 claim line, according to Thai officials, extends across the island, a move Bangkok calls legally baseless.
Yet even this land-sea distinction is disputed. Cambodia insists its maritime claim is rooted in the continental shelf — not island sovereignty — and that referring to Ko Kut is a deliberate distraction. Thai officials, in turn, accuse Phnom Penh of conflating two separate legal frameworks to gain leverage.
Lessons from the past
Cambodia is pointing to the 2016 Timor-Leste v. Australia conciliation as proof that non-binding recommendations can lead to lasting treaties — including revenue-sharing models. That process ended with a legally binding agreement just 14 months later.
Thailand, however, highlights different precedents: the 2012 Bangladesh v. Myanmar ruling by ITLOS, which adjusted equidistant lines for coastal geometry, and the 2009 Ukraine v. Romania case, which showed how complex gulfs can be partitioned using technical data — not political compromise.
What happens next?
The five-member commission, overseen by the Permanent Court of Arbitration, will now spend the next year reviewing technical submissions, bathymetric charts, and historical documents from both sides. Final recommendations are due by late 2027.
For Thai and Cambodian fishermen, oil explorers, and coastal communities, the status quo remains unchanged. No new drilling permits have been issued. No new border patrols have been deployed. And no economic zone has been formally recognized.
The real cost of the deadlock? A year without revenue from untapped resources — and the risk that further diplomatic friction could chill foreign investment in a region that once promised to be Thailand’s next energy hub.
