BHP Billiton has received first-round bids for its US shale portfolio from oil majors including BP and Chevron, valuing the unit at $US7 billion to $US9 billion ($9 billion to $12 billion), people familiar with the matter said.

Royal Dutch Shell, partnering with private equity firm Blackstone Group LP, also submitted a bid for the entire unit late in May, said the people, asking not to be identified because the information is private. Chevron has teamed up with another private equity firm, while BP is pursuing them alone, the people said.

Multiple parties, including private equity firms such as Apollo Global Management as well as energy companies, have bid separately for individual packages of shale real estate being sold by the Melbourne, Australia-based commodities giant, the people said.

BHP expects to receive about $US10 billion or more as bidding for the entire unit proceeds to a second round and as much as $US13 billion if it sells the assets piecemeal, the people said. The company prefers to sell the unit to a single party and expects to invite second-round bids as early as July, the people said.

An Apollo representative didn't immediately respond to a request for comment. BHP, BP, Chevron, Shell and Blackstone declined to comment.