BP's talks with AAR about the British oil firm buying out its Russian partner in joint venture TNK-BP "have now more-or-less collapsed", according to reports.
It comes ahead of BP's AGM later today and after the deadline for it to complete a $16bn (£10bn) share swap with Russian oil giant Rosneft was extended until 16 May.
The Russian billionaire shareholders of TNK-BP have argued that the Rosneft tie-up breaks promises BP made to them.
In a bid to placate AAR, BP offered to purchase its 50% holding in TNK-BP.
However the BBC says "a BP source said AAR put an impossibly high valuation on TNK-BP of around $70bn, which would value the oligarchs' stake at more than $35bn".
The news service reports BP was prepared, jointly with Rosneft, to pay something over $25bn for their stake, on the basis that TNK-BP is worth more than $50bn.
Meanwhile, protestors and angry shareholders intend to make their feelings known at today's AGM in London.
It is almost one year since 11 workers were killed when a drilling rig leased by BP exploded in the Gulf of Mexico, unleashing millions of barrels of oil.
Fishermen from the US are set to be among protesters at the AGM, the BBC reports.
Two global vehicles
'Further plug advice gap'
Must appoint separate CEOs and boards
Advisers do come out well
Will report to Mark Till