Houston-based oil and gas company Apache Corporation said late Thursday it has agreed to sell its operations in the Gulf of Mexico's shelf to a portfolio company of energy-focused private equity firm Riverstone Holdings in a deal worth $3.75 billion.

Riverstone's Fieldwood Energy, which is also based in Houston, will acquire Gulf assets comprising more than 1.9 million net acres. At the end of last year, those reserves held 239 million barrels of oil equivalent, 55 percent of which is oil and more than 75 percent of which is already developed, according to Fieldwood's separate announcement. As part of the agreement, Apache and Fieldwood will also jointly own the assets' exploration blocks and the two parties will work together to develop deepwater locations in the Gulf.

The deal is expected to close by the end of September, pending regulatory approval.

Apache's longtime outside M&A counsel, Bracewell & Giuliani, is once again leading the way for the company on this sale. The firm advised Apache last year on its $2.85 billion purchase of Cordillera Energy Partners III from a group led by EnCap Investments in a deal that more than doubled Apache's energy holdings along the Texas-Oklahoma border. That deal was Houston-based Apache's largest acquisition since its 2010 purchase of $7 billion worth of oil and gas assets from BP. Bracewell also advised Apache on that transaction.

For the sale to Fieldwood, Apache has turned to a Bracewell team that includes business and regulatory chair G. Alan Rafte, finance partner Kristen Campana, labor and employment partner Bruce Jocz, tax partner Elizabeth McGinley, and corporate and securities partners Bryan Loocke and Robin Miles. The Bracewell associates working on the deal are Stephen Boone, Michael De Voe Piazza, Laura Martone, and Christopher Miller.

Apache's general counsel is P. Anthony Lannie.

Teams from Simpson, Thacher & Bartlett and Vinson & Elkins, meanwhile, are representing Fieldwood. Simpson Thacher banking and credit partners Christopher Brown and Robert René Rabalais are working on the matter, along with associate Hayley Urkevich Nivelle.

Earlier this year, Simpson Thacher represented Riverstone Holdings on its acquisition of financing in connection with its purchase of Utex Industries for an undisclosed amount.

V&E's team is being led by New York–based M&A partner David Cohen, along with corporate partner Marc Rose and energy partner Shay Kuperman as well as associates Alan Alexander, Scott Fulford, Carson Sieving, and Mingda Zhao. Also advising is M&A partner Edward "Ted" Stockbridge, labor and employment partner Sean Becker, finance partner Christopher Dawe, environmental partner Larry Nettles, energy regulatory partner James Olson, and tax partners David Peck and David D'Alessandro.

V&E served as cocounsel to Riverstone and Apollo Management last year when the two private equity firms led a $7.15 billion leveraged buyout of El Paso Corporation's oil and gas exploration and production units.