The underlying issue centers on a 60-square-mile area of the Gulf, rich in potential oil and gas reserves, claimed by both nations. Thailand, maintaining its position since 1962, asserts its claim based on its interpretation of UNCLOS and previous demarcation agreements. Cambodia, bolstered by support from China, contends that its claim is based on historical fishing rights and the Treaty of Peace, arguing that Thailand’s interpretation is a colonial imposition. This contention is further complicated by China’s expanding naval presence in the region, generating anxieties about Beijing’s strategic influence. “The OCA isn’t just about oil,” stated Dr. Arun Kohlay, Senior Fellow at the Institute for Strategic Studies in Singapore. “It’s a proxy for broader geopolitical competition and a test of sovereignty in the face of rising global power.”
Historical context is crucial. The 1960 Treaty of Peace, signed after decades of armed conflict, established a basic maritime boundary but failed to definitively address the OCA. Subsequent interpretations of this treaty, influenced by evolving international law and the rise of hydrocarbon exploration, have deepened the divide. The 2011 Permanent Court of Arbitration ruling, largely unfavorable to Thailand, was rejected by Cambodia, further solidifying its position and triggering a series of aggressive actions, including the deployment of Cambodian naval vessels to the disputed area, leading to numerous confrontations with the Thai Royal Thai Navy. Data from the International Energy Agency (IEA) suggests that the OCA could contain significant untapped oil reserves, estimated between 4.3 and 8.7 billion barrels, intensifying the economic stakes.
Key stakeholders are clearly delineated. Thailand, led by Deputy Prime Minister and Minister of Foreign Affairs, Sihasak Phuangketkeow, is pursuing a multi-faceted strategy, combining diplomatic efforts, legal preparation under UNCLOS, and naval deterrence. Cambodia, under Prime Minister Hun Sen, is leveraging support from Beijing, receiving naval assistance and political backing. China’s involvement represents a significant strategic calculation – bolstering its “String of Pearls” maritime network and challenging what it perceives as Western influence in Southeast Asia. ASEAN, while attempting to mediate, has struggled to achieve a resolution due to the entrenched positions of the parties. The International Tribunal for the Law of the Sea (ITLOS) issued a non-binding ruling in 2014, reaffirming the ambiguity of the boundary, further exacerbating the situation.
Recent developments in the past six months demonstrate a heightened state of tension. In March 2026, Thai naval vessels engaged in a near-miss confrontation with Cambodian patrol boats, raising fears of an open conflict. Cambodia, citing “provocations” by the Thai navy, increased the number of its vessels patrolling the OCA. Furthermore, Thailand initiated preparations for compulsory conciliation under UNCLOS, a legally binding process intended to resolve the dispute through international arbitration, a move seen as a deliberate escalation by Cambodia. According to a report by the Control Risks Group, “The increased naval activity and the initiation of conciliation proceedings suggest Thailand is preparing for a protracted confrontation and a willingness to defend its claims vigorously.”
Looking ahead, the next 6-12 months are likely to see continued naval deployments, heightened diplomatic friction, and a strengthening of legal preparations by both sides. A genuine resolution seems improbable without significant compromise, particularly given the substantial economic interests at stake. Long-term, the situation could escalate into a protracted maritime conflict, potentially drawing in regional powers. The potential for miscalculation remains high, exacerbated by China’s expanding naval presence and its willingness to support Cambodia. Beyond the immediate OCA dispute, the situation underscores broader challenges to maritime governance and the interpretation of international law in contested waters. Furthermore, the resolution or non-resolution of this dispute will heavily influence the stability of ASEAN, a bloc increasingly under strain from competing national interests and geopolitical influences.
The “murk” of the Mekong’s maritime disputes presents a powerful, and perhaps unsettling, reflection of global geopolitical currents. The upcoming months will determine whether Thailand and Cambodia can manage this confrontation constructively or whether the OCA becomes a focal point for regional instability. The core question facing policymakers is whether the international community can facilitate a resolution based on principles of international law and peaceful dispute resolution, or whether this unresolved territorial claim will become another source of conflict in a rapidly changing world. It remains imperative that all stakeholders demonstrate restraint and prioritize diplomacy to avert a disastrous outcome.