[Editor's note: This story was updated from a previous version posted on 7:35 a.m. CST March 8.]

Royal Dutch Shell Plc (NYSE: RDS.A) and U.S. private equity firm Blackstone Group LP are working on a joint $10 billion bid for BHP Billiton Ltd.'s (NYSE: BHP) U.S. shale assets, Sky News said on March 8.

Shell and Blackstone's offer will only be one of several credible proposals that BHP will receive for its U.S. shale operations, Sky News said, citing banking sources.

BHP, Shell and Blackstone declined to comment.

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Private-equity companies have been active buyers of U.S. shale producing assets in recent years. This week, Devon Energy Corp. (NYSE: DVN) said it sold some shale-gas assets in Texas for $553 million to a buyer that Tudor, Pickering, Holt & Co. energy analysts identified as a private-equity firm. Devon did not disclose the name of the buyer.

BHP's acreage is located adjacent to assets controlled by Shell and Anadarko Petroleum Corp. (NYSE: APC) in the Permian Basin of West Texas and New Mexico. Anadarko bid late last year on BHP's onshore properties, according to two people familiar with the transaction.

Anadarko did not immediately respond to requests for comment.

Steve Pastor, BHP's president for petroleum operations, said this week the company would consider swapping certain onshore oil and gas assets with competitors' offshore assets as part of its effort to exit U.S. shale operations.

BHP, the world's largest miner, said last month it expected to receive initial bids for the operations in the June quarter.

The company last year said it would exit its underperforming U.S. shale oil and gas business after coming under pressure from Sydney-based Tribeca Investment Partners to sell the assets.

Activist hedge fund Elliott Management has also called for BHP'S exit from shale to free up capital.