Royal Dutch Shell is working with the private equity firm Blackstone Group on a $10 billion (£7.2 billion) bid for BHP Billiton’s US shale assets.

The Anglo-Dutch oil group first expressed interest in the assets, some of which neighbour its own existing shale fields in the Permian basin, last month.

It has now teamed up with the private equity giant to work on a joint offer, Sky News reported last night. Shell and Blackstone both declined to comment.

Shell is seeking to expand its shale business, which it identified last year as a key growth opportunity, while BHP, the Anglo-Australian mining group, is looking to offload its underperforming shale division under pressure from the activist investor Elliott Management.

BHP expects to receive initial bids in…