Labour hate the idea of independence as that'll mean they lose loads of seats in Westminster and the Tories will lose none. It would make it harder for Labour to win a general election for England & Wales.
I wonder how many Scots would vote for independence when they realise that they'd no longer get the financial advantage from the Barnett formula. (which is worth more that oil revenue in Scottish waters)
EDIT
Where would they draw the line for ownership of the oil?
MAP CLICKY(Warning, 5mb download.)
If they followed the line of the boarder, the English would get quite a lot. However I expect the Scots would want it to follow 56 degrees North.