BP's net debt has fallen to US$13.9 billion, allowing it to reach its net debt target a year ahead of schedule. (EPA Images pic)LONDON: Former Shell CEO Ben van Beurden will chair Castrol's board after Stonepeak completed its acquisition of a 65% stake in the lubricants maker from BP on Monday, the US private equity firm said.

BP agreed the stake sale last year and will retain a 35% stake in a new joint venture with Stonepeak.

The oil major separately confirmed on Monday that it would use US$6 billion in after-tax proceeds to trim debt and bolster its finances.

"This deal brings meaningful cash proceeds to bp today while retaining a valuable stake in Castrol’s future growth," BP chief executive Meg O'Neill said in a statement.