... also, the target formations are shallower in OBL's Derby...

... also, the target formations are shallower in OBL's Derby block, because of historical erosion of higher formations. So they went just as deep as further east, so they should have been 'cooked' the same (ie. same prospectivity for oil/gas), but the upper formations were then eroded by glaciers (it was then down by the south pole). Why is this relevant? - it means that OBL can use a smaller, more mobile and much cheaper rig than Buru, in order to reach the same formations. So why haven't they done any drilling to date? They had no money ... which is why the FMG deal is good despite having to give up a 25% interest (ie. you can own 50% of nothing, since you can't drill, or you can own 25% of a free carry which might find something).