bul london investor presentation 16 july 09, page-16

The answer is which one can be commercialised first.
BUL have an agreement with Stanwell that requires Stanwell to pay costs associated with drilling the first area and Stanwell will be in a position to take gas produced. This will give BUL early income.
Proving reserves will take time in the 813p area. It will also be some time before the expost facilities are available for the Kogas deal to pay off.

So it is a case of get some early income to fund the major prospects.