The Thailand–Malaysia maritime boundary dispute and the future of the joint development area: A comparative assessment with the Somalia–Kenya case

The Joint Development Area established by the 1979 Memorandum of Understanding between Thailand and Malaysia will expire in 2029. The Memorandum preserves the parties’ competing sovereignty claims, while the underlying maritime boundary dispute has remained unresolved for over fifty years. As 2029 approaches, the dispute may be submitted to international adjudication. This study offers an original contribution by examining the Thailand-Malaysia dispute through international jurisprudence on maritime delimitation, using Somalia-Kenya as its principal comparator. Both cases involve adjacent States whose coasts are concave, which permits the coastal geometry at issue to be examined by close analogy. The analysis addresses three questions. First, how does the geographical distinction between the cases—Kenya’s coast was enclosed between Somalia and Tanzania, whereas Thailand delimits only with Malaysia—affect any claim to adjust an equidistance line? Second, can hydrocarbon resources in the disputed area constitute an independent relevant circumstance under established ICJ and ITLOS jurisprudence? Third, how should Ko Losin be characterised under Article 121 of UNCLOS, and what effect should it receive in delimitation? The study concludes that Thailand’s concavity provides a materially weaker basis for adjustment than Kenya’s because Thailand is not compressed between two flanking States; any adjustment in Thailand’s favour would therefore be modest at most. On the presently available site-specific record, Ko Losin satisfies Article 121(1) but falls within Article 121(3) and is unlikely to receive full or controlling base-point effect. If adjudicated, the provisional equidistance line is likely to favour Malaysia, although any subsequent adjustment would remain fact-sensitive.