Brunei is composed of two discontinuous territories on the island of Borneo, bisected by a strip of Malaysian territory in the Limbang Valley that extends to Brunei Bay. Aside from its northwest facing coastlines, Brunei’s territory is completely encompassed by Malaysia.  As a result, Brunei and Malaysia share three maritime boundaries. A four nautical mile long boundary lies in the Brunei Bay and connects the land boundary termini on either side of the Limbang Valley. Two lines extending from Brunei’s outer land boundary termini into the South China Sea make up the remaining maritime boundaries.

The current boundaries of Brunei’s and Malaysia’s territorial waters and continental shelves extend up to the 100 fathom isobath and are based on two 1958 Orders in Council made by the United Kingdom. At the time, Brunei was a British protectorate which gave the United Kingdom control over its foreign affairs. The adjacent colonies of Sarawak and North Borneo, which would later become part of Malaysia, were also administered by the United Kingdom. The 1958 Orders were accepted by both States following their independence.

In 2009, Brunei and Malaysia signed an exchange of letters that resolved some of their outstanding maritime boundary issues. While the contents of the documents have never been made public, they reportedly include the delimitation of the territorial sea, the exclusive economic zone and the continental shelf boundaries out to a distance of 200 nautical miles.

Brunei and Malaysia have an established land boundary.