Pioneer Corp. received an acquisition proposal.

Under the offer from Mesa Limited Partnership, Pioneer would receive about 58.1 million “Pioneer-A” preference units and 33.2 million “Pioneer-B” units of Mesa Limited Partnership in exchange for all of its assets and businesses, including the assumption of all liabilities other than those arising as a result of the deal. Pioneer then would distribute the units to its shareholders pursuant to the liquidation plan previously adopted by the board. Industry sources valued the offer at $25 million to $28 million.