LONDON/NEW YORK (Reuters) -BP is in active talks with investment firm Stonepeak over the sale of its Castrol lubricants unit, two people with knowledge of the situation said, in what would be a major step in meeting the energy company's $20 billion divestment goal.

KEY DETAILS

-- Both Stonepeak and private equity firm One Rock made bids for the unit in September, one of the people and a third one said. Reuters could not establish the value or structure of Stonepeak's consideration or if BP is currently in talks with other parties including One Rock about a deal for Castrol. A deal may not materialize, the people said. 

-- Reuters reported in May, citing sources, that BP had kicked off the sale of Castrol.

-- RBC analysts said in recent weeks that market expectations for the sale are around $8 billion.  

-- BP, Stonepeak and One Rock representatives declined to comment.  

WHY IT MATTERS

-- The sale is part of BP's strategy shift to refocus as it tries to boost profitability and fend off pressure from investors including activist hedge fund Elliott.  

-- BP CEO Murray Auchincloss said earlier this month the interest in Castrol is "very high" but declined to comment on specifics. He added he expects completed or announced asset sales to total around $5 billion this year.