Australia–Indonesia Border - The Border

The Border

The boundary is separated into three segments, with the first two broken by the Timor Gap. The first is between the Australia – Indonesia – Papua New Guinea tripoint at 10° 50' S, 139° 12' E, and the point whether the territorial waters of the two countries touch the eastern limits of the territorial waters claimed by East Timor at 9° 28' S, 127° 56' E. The second segment runs westward from the point where the territorial waters of the two countries touch the western limits of East Timor's territorial waters claim at 10° 28' S, 126° 00' E, to 13° 05' 27.0" S, 118° 10' 08.9" E in the Indian Ocean. The third is between the Australian external territory of Christmas Island and the Indonesia island of Java, in the Indian Ocean.

The boundary is established by three treaties, the third of which has been signed but not yet ratified. The Agreement between the Government of the Commonwealth of Australia and the Government of the Republic of Indonesia establishing Certain Seabed Boundaries signed in Canberra on 18 May 1971 established part of the eastern segment of the seabed boundary (as well as Indonesia's maritime boundary with Papua New Guinea in the Torres Straits) while the Agreement between the Government of the Commonwealth of Australia and the Government of the Republic of Indonesia establishing certain seabed boundaries in the area of the Timor and Arafura Seas, Supplementary to the Agreement of 18 May 1971 which was signed in Jakarta on 9 October 1972 demarcated the rest of the eastern segment and a portion of the western segment of the seabed boundary. The third treaty, the Treaty between the Government of Australia and the Government of the Republic of Indonesia establishing an Exclusive Economic Zone Boundary and Certain Seabed Boundaries (informally known as the Australia–Indonesia Maritime Delimitation Treaty) which was signed in Perth on 14 March 1997, extended the western segment of the seabed boundary to its termination point in the Indian Ocean.

The basis for establishing the boundary in the 1971 and 1972 treaties was that of the "natural prolongation" of the physical continental shelf. This resulted in the boundary running significantly north of the median line between the shores of Australia and Indonesia, thus benefiting Australia in terms of the division of the seabed ownership. The International Law view of settling overlapping claims has then moved towards the median-line concept, although Australia still holds the view that natural prolongation was still relevant to determine the sovereignty of the seabed. This resulted in the separate treatment of establishing the seabed boundary and that for the water column, or essentially, the separation of the continental shelf and exclusive economic zone boundaries under the 1997 treaty.

The independence of East Timor on 20 May 2002 may result in changes in the Australia–Indonesia border near the Timor Gap which were established by the three treaties. Provisions of the 1997 treaty on matters concerning the Timor Gap – such as reaffirming the Timor Gap Treaty between Australia and Indonesia and the drawing of the water column boundary through the area of joint development – would no longer be applicable with East Timor becoming the rightful claimant of the seabed and exclusive economic zone in the area. Furthermore, the "Timor Gap terminal points" established by the 1972 treaty, namely Points A16 and A17, might have to be renegotiated by Australia, East Timor and Indonesia, as East Timor might have the basis to seek a "wider" Timor Gap than originally provided by Australia and Indonesia.