The maritime boundary between Indonesia and Malaysia consists of four discontinuous sections due to the complicated coastal geography of the two countries. Malaysia’s territory is split between the southern Malay Peninsula and a large part of the island of Borneo, lying across the southern portion of the South China Sea.

Indonesia is an archipelagic State that is composed of hundreds of islands that extend along a generally east-west axis. One of its principal islands, Sumatra, lies directly across the Strait of Malacca from mainland Malaysia.

The fragmented territories of the two States and the proximity to neighboring States result in many maritime boundary termini located near waters that pertain to third States. Malaysia and Indonesia have an established tripoint with Thailand in the Strait of Malacca. There are two potential tripoints with Singapore in the Singapore Strait. Further east there are two tripoints that have been agreed to with Vietnam in separate bilateral Agreements and another provisional tripoint with the Philippines in the Celebes Sea.

Indonesia’s and Malaysia’s maritime boundaries are comprised of four segments, all having been only partially established. In the Strait of Malacca, a 432 nautical mile (M) continental shelf and territorial sea boundary has been agreed to. To the east, a 315 M segment on the western side of Natuna Islands in the South China Sea exists between the two States, and there is a 259 M segment on the eastern side of the Natuna Islands. The two States have an additional fourth area of overlapping maritime claims in the Celebes Sea at the eastern end of the island of Borneo, which has yet to be fully defined. The maritime boundaries in the Strait of Malacca and the South China Sea were first delimited in a 1969 continental shelf Agreement. The territorial sea boundary in the Strait of Malacca was delimited in 1970. The continental shelf boundary was extended in the Strait of Malacca to the tripoint with Thailand in a 1971 trilateral Agreement. Two treaties were signed in 2023 that delimit parts of the territorial seas in the Strait of Malacca and the Celebes Sea. Indonesia and Malaysia have yet to agree to any exclusive economic zone boundaries.

Indonesia and Malaysia also have an established land boundary.

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