Setting the Boundaries in the Timor Sea: The Prospects of Renewed Negotiations between Australia and East Timor – Esther Pearson

The issue of maritime boundaries in the Timor Sea is once again live following a request from East Timor’s Prime Minister, Rui Araugj, to Prime Minister Malcolm Turnbull that the leaders meet to discuss a permanent maritime boundary. According to Dr Araujo, the existing arrangements governing the exploitation of gas and oil resources in the Timor Sea are not consistent with East Timor’s entitlements under international law. Mr Turnbull has offered to hold ‘frank and open’ discussions about the border, while the Shadow Minister for Foreign Affairs, Tanya Plibersek, has said that the Australian Labor Party, if successful at the Federal election, would negotiate in ‘good faith’ and would submit the matter to international arbitration if negotiations were to fail. This article discusses the background to the dispute and the current arrangements between Australia and East Timor, as well as the possible outcome of any arbitration.

Background and Current Arrangements

In 1972, Australia and Indonesia entered an agreement on maritime boundaries in the Timor Sea, with the final boundary being divided into two sections separated by a gap, in recognition of the existence of what was, at the time, Portuguese Timor. The gap became known as the ‘Timor Gap’, and the ‘Timor Gap Zone of Cooperation’ was established between Australia and Indonesia. On 20 May 2002, the date of East Timorese independence, Australia and East Timor entered into the ‘Timor Sea Treaty’ (‘TST’), which established a Joint Petroleum Development Area (‘JPDA’) over the central part of the Zone of Cooperation. The southern boundary of the JPDA representing the median line between Australia and East Timor. Under Article 2 of the TST, the issue of maritime boundaries was set aside without prejudice to the States’ future rights to negotiate a permanent boundary. It was agreed that East Timor would receive 90% of the revenue from the exploitation of the gas and oil deposits in the JPDA and Australia would receive 10%.

On 6 March 2003, the Sunrise International Unitisation Agreement (‘Sunrise IUA’) was signed between Australia and East Timor that unitised the fields that straddled the eastern side of the JPDA into the ‘Greater Sunrise’ field. The Sunrise IUA deemed 20.1% of the field to lie within the JPDA, meaning that, as East Timor was to receive 90% of the revenue under the TST, it would receive 18.1% of the revenue from the Greater Sunrise field. East Timor considered this arrangement to be unacceptable and refused to ratify the agreement.

Negotiations concerning the exploitation of the Greater Sunrise field resumed in 2004, eventuating in the signing of the Treaty on Certain Maritime Arrangements in the Timor Sea (‘CMATS’) on 12 January 2006. Article 2 of CMATS provides that the treaty is without prejudice (inter alia) to the States’ legal position regarding maritime boundaries, while Article 12 defers each States’ boundary claims for up to 50 years. Under Article 5, Australia and East Timor are to share the revenue from the exploitation of the field equally, despite that around 80% of the field lies outside the JPDA and within Australia’s continental shelf.

Legal Context

The key legal instrument governing the law of the sea is the United Nations Convention on the Law of the Sea (‘UNCLOS’). Articles 56 and 57 of UNCLOS allow States to declare an Exclusive Economic Zone (‘EEZ’) of up to 200 nautical miles (‘nm’), in which the State has sovereign rights to explore, exploit, converse and manage natural resources in the seabed, subsoil and water column. Articles 76 and 77 entitle States to a continental shelf that extends to the outer edge of the continental margin, or to a distance of 200 nm from the territorial sea baseline, in which the State has sovereign rights to explore and exploit the seabed and subsoil.

In the case of States with opposite coasts less than 400 nm apart, it is necessary for the States to agree, or for an independent body to decide, on the delimitation of the States’ maritime boundaries. Article 74 of UNCLOS relevantly provides (inter alia) as follows:

  1. ‘The delimitation of the exclusive economic zone between States with opposite or adjacent coasts shall be effected by agreement on the basis of international law, as referred to in Article 38 of the State of the International Court of Justice, in order to achieve an equitable solution.
  2. If no agreement can be reached within a reasonable period of time, the States concerned shall resort to the procedures provided for in Part XV.

Article 83 of UNCLOS addresses the delimitation of the continental shelf and is substantially in the same wording as Article 74.

The Current Situation

East Timor asserts that the north/south boundary between Australia and East Timor should be determined on the basis of equidistance. Given that the southern boundary of the JPDA represents the median line between the States, this would effectively bring the entirety of the JPDA within East Timor’s EEZ. East Timor also wants to shift the eastern and western laterals (the sides of the JPDA) further in each direction. This would bring a greater proportion of the Greater Sunrise field within the JPDA.

Australia, on the other hand, has traditionally argued that the delimitation of continental shelves in the Timor Sea should reflect the ‘natural prolongation’ of each States’ land territory under the sea. This would lead to the formation of two separate continental shelves separated by the Timor Trough, with Australia’s continental shelf extending significantly further than that of East Timor. Australia also refutes East Timor’s claims to the east and west of the JPDA. These opposing attitudes are likely to make it difficult for an agreement to be reached through negotiation.

Articles 74(2) and 83(2) of UNCLOS provide that if no agreement can be reached through negotiation, the States should resort to the procedures enshrined in Part XV. Under Part XV, each State that accedes to or ratifies UNCLOS is to choose whether any dispute will be submitted to the International Tribunal for the Law of the Sea (‘ITLOS’), the International Court of Justice (‘ICJ’) or an arbitral tribunal. On 21 March 2002, in submitting to the jurisdiction of ITLOS and the ICJ, Australia declared that it did not accept any of the dispute resolution procedures in the case of maritime boundary disputes. On 25 March 2002, Australia made a reservation under Article 36(2) of the Statute of the International Court of Justice as to the jurisdiction of the ICJ to resolve disputes over maritime boundaries.

Possible Outcome of Arbitration

This leaves East Timor with the possibility of submitting the matter to international arbitration, should the Australian government be willing. While the arbitrator/s would not be bound by the jurisprudence of ITLOS and the ICJ, the principles established by these bodies are likely to have some influence on the outcome. Despite the finding of the ICJ in North Sea Continental Shelf (Federal Republic of Germany/Netherlands) that natural prolongation should be a significant factor guiding the delimitation of the continental shelf, more recently, the concept of equidistance has been given primacy (see, in particular, Continental Shelf (Libyan Arab Jamahiriya/Malta)).

In its judgment in Maritime Delimitation in the Black Sea (Romania v Ukraine), the ICJ developed a three-step approach to the delimitation of States’ boundaries with opposite coasts. Firstly, a provisional median line is drawn between the coastal States. Secondly, any factors that require an adjustment to the provisional line to achieve an equitable result are considered. Finally, to ensure the result is equitable, the ratio between the States’ coastal lengths and maritime areas, with reference to the adjustment line, are compared. As there are no obvious factors requiring an adjustment to the provisional median line between Australia and East Timor, it is reasonable to expect any arbitral tribunal to find in favour of an equidistant north/south boundary.

In terms of the eastern and western JPDA laterals, an opinion prepared by three public international law specialists, Vaughan Lowe, Christopher Carleton and Christopher Ward, considers that the laterals should move further in each direction. According to the opinion, the western lateral proceeds from the incorrect point on East Timor, and, should the lateral proceed from the correct point, the line would move somewhat to the west. In addition, the eastern lateral gives disproportionate effect to the western Indonesian island of Leti. This means that all points on the lateral are equidistant between East Timor and Leti, resulting in the eastern boundary being closer to East Timor. If half or three-quarters effect were given to Leti, consistent with ICJ jurisprudence (see Continental Shelf (Tunisia/Libyan Arab Jamahiriya), the eastern lateral would move significantly to the east, placing most, or all, of the Greater Sunrise field with East Timor’s EEZ. This also points towards an arbitral tribunal finding in favour of East Timor.


The issue of maritime boundaries in the Timor Sea is the cause of considerable tension between Australia and East Timor. The foregoing analysis suggests that East Timor’s Prime Minister may, in fact, be correct to say that the existing arrangements do not reflect East Timor’s entitlements under international law. With this in mind, the outcome of the upcoming Federal election may bring about a significant change in the relationship between the two Asia-Pacific neighbours.

Esther Pearson is Assistant Editor of the ILA Reporter.