Brunei–Malaysia border which are defined by agreements, from west to east, are as follows: Brunei and Malaysia in an Exchange of Letters on 16 March 2009, agreed to affirm the five agreements. The two countries also agreed to use the watershed principle to determine the remaining undelimited portions of the border. Brunei's maritime boundary with Malaysia until the 100 fathom isobath was inherited from the Sarawak (Definition of Boundaries) Order in Council 1958 No 1518 and the North Borneo (Definition of Boundaries) Order in Council 1958 No 1517, both of which defined the boundary between Brunei on the one hand, and Sarawak
Indonesia–Malaysia border the area. The dispute started with Malaysia issuing a map in 1979 of its territorial sea and continental shelf which included the Ambalat block. The map drew Malaysia's maritime boundary in a southeast direction into the Celebes Sea after it leaves the eastmost point on land on Sebatik island. This would include the Ambalat block, or a large part of it, within the Malaysian continental shelf. Indonesia has, like the other neighbours of Malaysia, objected to the map. Indonesia has never officially announced the exact locations of its maritime boundaries but claimed during its arguments in the Sipadan Case that