Huntsman Corp., the chemical maker seeking to force completion of a $6.5 billion buyout by Hexion Specialty Chemicals Inc., hired a valuation firm to provide an opinion that the combined company would be solvent.

American Appraisal Associates Inc. will provide a written opinion that the merged assets of Hexion and Huntsman will exceed liabilities, according to an agreement filed today with regulators. Huntsman will pay $1 million to Los Angeles-based American Appraisal, with an additional fee to be negotiated should the opinion be delayed past Nov. 1.

Huntsman and Hexion, a unit of New York-based Apollo Management LP, argued this month in Delaware Chancery Court over Hexion's bid to scuttle the merger. Hexion got an opinion from Duff & Phelps LLC that said the combined company would be insolvent because of Huntsman's deteriorating finances.

American Appraisal previously provided valuation services to Hexion, according to the agreement. Huntsman is run from The Woodlands, Texas, and Salt Lake City.