A drilling rig of Cobalt International Energy.

At least a half-dozen law firms, including some titans of the Am Law 100, are collectively owed more than $3.5 million in fees following a bankruptcy filing on Dec. 14 by Cobalt International Energy Inc.

The Houston-based oil exploration and production company began Chapter 11 proceedings in its home city this week as a result of a crushing $2.8 billion debt load, slumping oil prices and the ultimately unsuccessful $1.75 billion sale of Cobalt’s operations in the oil-rich African nation of Angola, a matter in which Cobalt was advised by Baker Botts. The latter subsequently took the lead for the company as federal regulators probed Cobalt’s activities in Angola.

According to a list of Cobalt’s 30 largest unsecured creditors, the debtor owes nearly $2.78 million to Skadden, Arps, Slate, Meagher & Flom; nearly $1.12 million to Wachtell, Lipton, Rosen & Katz; $537,956.65 to Williams & Connolly; $79,008.60 to Gardere Wynne Sewell; $23,658.73 to Covington & Burling; and $10,533.75 to Vinson & Elkins.

Skadden is representing underwriters in class action litigation involving Cobalt, which has been sued by shareholders for allegedly misrepresenting the value of its assets in Angola, where the company has been accused of bribing local officials. The U.S. Department of Justice closed an Angola-related inquiry into Cobalt earlier this year, while a parallel civil probe by the U.S. Securities and Exchange Commission was dropped in 2015.

But securities litigation against Cobalt continues in a Houston federal court, which in June certified a class pursuing claims against the company. Williams & Connolly is counseling private equity giant The Carlyle Group LP, a key shareholder in Cobalt, as is Riverstone Holdings LLC, which is being advised by Wachtell. The firm is also representing several other parties in the litigation.

Gardere—reportedly in merger talks with Foley & Lardner—is representing Riverstone, Carlyle and more than a half-dozen other defendants in the case. Vinson has previously advised Cobalt on its operations in Angola and matters related to the Foreign Corrupt Practices Act.

Kirkland & Ellis and Houston-based solo practitioner Zack Clement—a retired Fulbright & Jaworski partner who has previously worked at Sidley Austin and Weil, Gotshal & Manges—have been retained to represent Cobalt in Chapter 11 proceedings. Neither firm has yet filed billing statements with the bankruptcy court.

Taking the lead for Kirkland, which within the past year has been busy handling a number of energy industry bankruptcies, are restructuring partners James Sprayregen, Chad Husnick, Marc Kieselstein and Brad Weiland, as well as litigation partners Gabor Balassa and Stacy Pepper. Kirkland, which recently submitted a final bill for $76.9 million in fees for its work in the bankruptcy of Caesars Entertainment Operating Co., also picked up a lead role this week in the Chapter 11 case of Houston-based fashion jewelry chain Charming Charlie Holdings Inc.

Cobalt, which said it has enough money to continue its operations in Chapter 11, raised $850 million through an initial public offering in December 2009. Securities filings at the time show that the listing generated $2 million in legal fees and expenses for Cobalt’s lawyers at Davis Polk & Wardwell. Shearman & Sterling took the lead for underwriters on the offering. Cobalt’s general counsel is Baker Botts and Vinson alum Jeffrey Starzec.

Earlier this month, the bankruptcies of three other energy companies left a host of large firms awaiting payments for outstanding legal bills.