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
Peninsular Malaysia Peninsular Malaysia Peninsular Malaysia also known as Malaya or West Malaysia, is the part of Malaysia which lies on the Malay Peninsula and surrounding islands. Its area is , which is nearly 40% of the total area of the country - - or slightly smaller than England and Java island. It shares a land border with Thailand in the north. To the south is the island of Singapore. Across the Strait of Malacca to the west lies the Sumatra Island (Indonesia) and across the South China Sea to the east lies the Natuna Islands (Indonesia). Peninsular Malaysia accounts for the