Labor shadow foreign minister Tanya Plibersek has committed a future Labor government to negotiations with the Timor Leste government to reach a permanent maritime border between our two countries, and undertaken to hand the issue over to UNCLOS arbitration if an agreement cannot be reached.

This might seem a sensible way to go. The East Timorese have certainly been victims of some awful history. They are poor and we are rich. An equidistant border seems intuitively fair. Our bumbling Inspector Clouseau spying efforts are an ongoing national disgrace.

But there is a fair bit of misunderstanding about the relevant geography

Popular commentary sees the central issue as an equidistant border. Typical is Tom Allard, who writes about this often in the Sydney Morning Herald:

If the boundary was drawn midway between East Timor and Australia — as is standard under international law — most of the oil and gas reserves would lie within Timor's territory.

As a geographical fact about known petroleum resources, this is wrong. Look at the map showing the location of the main oil resource — Greater Sunrise — with estimated revenues of $40 billion. Some 80% of this undeveloped field is to the east of the Joint Petroleum Development Area (JPDA). Shifting the boundary to equidistant still leaves 80% of Sunrise in Australian territory. True, Timor would then have 100% of the JPDA revenue from resources that lie north of an equidistant border, but at the moment they receive 90% of the revenue from resources currently being exploited, and under the existing agreement would receive 50% of the overall Sunrise revenue (not just the part of Sunrise which lies in the JPDA).

For Timor to get a larger share of Sunrise, the border on the east side of the JPDA would have to be shifted eastward. Of course that would have to involve Indonesia: the eastern edge of the JPDA is based on equidistance between Timor and the Indonesian islands to the east of Timor. But why would Indonesia agree to such a shift? Sunrise is closer to Indonesia than it is to Timor.

If this issue goes to UNCLOS and the East Timor/Australia border is shifted to equidistant, Indonesia will probably demand that its border be shifted to equidistant. The same arguments apply in this case: that border was decided at a time when Indonesia was weak and Australia was strong. At that time, a border based on the continental shelf was normal, but now the fashion has changed so the UNCLOS arbitrators, unable to decide in the more common case where the continental shelf is not well defined, take the easy way out and settle for equidistant. That would put 80% of Sunrise  in Indonesian territory and it seems unlikely that Indonesia would give Timor any share of the revenue.

Is this such a bad outcome? After all, Indonesia has many more poor people than Timor has. But it may not be what the Labor Party has in mind.