A $16bn (£10bn) share exchange between BP and state-owned Russian counterpart Rosneft has been blocked again.
An arbitration panel upheld an injunction on the deal, but gave BP more time to hammer out a solution.
Russian shareholders of TNK-BP - an earlier joint venture of the UK firm - have argued that the Rosneft tie-up breaks undertakings BP made to them.
The injunction against the share swap and a related Arctic exploration deal was already confirmed once last month.
Following that earlier ruling - which blocked the entire package of agreements with Rosneft - BP asked the arbitration panel to reconsider the share swap as a separate stand-alone deal.
Under the deal, Rosneft would take five per cent of BP in exchange for about 9.5 per cent of Rosneft.
The UK oil firm had been up against a tight deadline, with its agreements with Rosneft needing to be consummated by 14 April, or else they would expire.