UPDATE: 3/1/13, 12:45 p.m. EST. Information on the names of the lawyers from Latham & Watkins advising Energy Transfer Equity has been added to the ninth paragraph of this story.

Latham & Watkins and a trio of Am Law 200 firms with Lone Star State roots are fueling up on the proposed $1.5 billion cash-and-stock sale of Southern Union Gathering to Regency Energy Partners.

The deal will allow Regency to expand its assets in the Permian Basin, an oil and natural gas rich region in western Texas and southeastern New Mexico. Reuters reports that the purchase by Regency includes a 5,600-mile gathering system and processing and treatment facilities for natural gas and natural gas liquids.

Locke Lord corporate partners Dan Fleckman and Van Jolas are leading a team from the firm advising Regency on the deal. Fleckman once served as chief legal officer for Regency before joining Locke Lord in 2011 from Mayer Brown.

Paul Jolas—a former Haynes and Boone partner and brother of Van Jolas—was tapped to become Regency’s chief legal officer and secretary in September 2009. He resigned that position last May, according to an SEC filing by the Dallas-based natural gas transportation company.

Christine LaFollette, partner-in-charge of Akin Gump Strauss Hauer & Feld’s Houston office and a member of the firm’s management committee, is representing a conflicts committee of Regency’s board of directors with respect to the Southern Union Gathering acquisition. Akin Gump energy partner John Goodgame is also working on the matter.

Southern Union Gathering is a jointly owned affiliate of the partnership between Dallas-based Energy Transfer Partners (ETP) and Energy Transfer Equity (ETE). An SEC filing by Regency detailing the contribution agreement under which it will take control of Southern Union Gathering shows that Andrews Kurth is advising the subsidiary on the transaction.

G. Michael O’Leary, cochair of Andrews Kurth’s corporate and securities practice and a member of its policy committee, is representing Southern Union Gathering on its proposed sale to Regency. In 2011, O’Leary advised a joint venture of Regency and ETP on their $1.9 billion acquisition of pipeline and natural gas liquids storage and processing plants, according to our previous reports.

Former Andrews Kurth partner Thomas Mason serves as general counsel and secretary for ETP. John McReynolds, a former partner at Hunton & Williams, serves as president and CFO for ETE. The sale of Southern Union Gathering to Regency is expected to close in the second quarter of this year, pending regulatory approvals and other closing conditions.

Latham corporate partners William Finnegan IV and Sean Wheeler, tax partner C. Timothy Fenn, and local finance practice chair Craig Kornreich in Houston—all of whom joined the firm in 2010 after it opened an office in the city—are advising ETE on the transaction. Wheeler, who serves as cochair of Latham’s oil and gas industry team, and Finnegan were named Dealmakers of the Week by The Am Law Daily in 2011 for their work representing ETE on its $4.2 billion purchase of Southern Union that year. Other Latham lawyers advising ETE on the current deal include associates Pamela Kellett, Cephas Sekhar, and Debbie Yee.

The Permian Basin has been a hot spot of late for Am Law 100 firms with robust energy practices. Akin Gump and Locke Lord grabbed roles advising Houston-based Linn Energy on its $4.3 billion buy of Berry Petroleum last week, while Mayer Brown and Vinson & Elkins took roles on a $1.7 billion investment in an oil and gas project in the Permian Basin by China’s Sinopec last month.