Malaysia–Thailand border

The Malaysia–Thailand border consists of both a land boundary across the Malay Peninsula and maritime boundaries in the Straits of Malacca and the Gulf of Thailand/South China Sea. Malaysia lies to the south of the border while Thailand lies to the north. The Golok River forms the easternmost 95 km stretch of the land border.

The land border is based on the 1909 treaty between Thailand, then known as Siam, and the British which started to exert its influence over the northern Malay states of Kedah, Kelantan, Perlis, Perak and Terengganu in the early 20th century. The four states had earlier been under Siamese control. Four Malaysian states abut the border. They are (from west to east) Perlis, Kedah, Perak and Kelantan. The four Thai provinces which abut the border are (again from west to east) are Satun, Songkhla, Yala and Narathiwat.

Malaysia and Thailand have a territorial sea and continental shelf boundary agreements for the Straits of Malacca which was signed in 1979 and 1971 respectively. The 1979 agreement also included Indonesia as a signatory as it also determined the common continental shelf border tripoint for the three countries. The 1979 agreement also established the territorial sea boundary in the Gulf of Thailand while a separate memorandum of understanding signed in 1979 established a short continental shelf boundary in the area. The boundary beyond that agreed is subject to dispute because of overlapping claims over the seabed. The overlapping claims led to the establishment of a joint development area in 1990 where both countries agreed to share mineral resources in a 7,250 square km wedge-shaped area.

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