The sources were unable to give details, but other sources familiar with the situation previously said the offer would be made to BP in cash and shares. "It will value the combined group at over $50 billion," said one.
The only other potential buyer, tycoon-led AAR, pulled out of the bidding on Wednesday and has offered its own 50-percent stake in the venture to Rosneft.
"BP is reviewing options," one of the sources said.
BP and Rosneft declined to comment.
(Reporting by Andrew Callus in London and Doug Busvine in Moscow, Writing by Sarah Young, Editing by Paul Sandle and Ben Hirschler)
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