As the U.S. moves to become the world’s largest oil producer, lawyers from a half-dozen Am Law 100 firms are helping QEP Resources unload its natural gas pipeline and processing unit to Tesoro Logistics, a refinery operator owned by Tesoro Corp.

Denver-based QEP announced Monday that its QEP Field Services unit would divest itself of its midstream assets—essentially the means of transporting oil and natural gas—to Tesoro Logistics for $2.5 billion in cash. Wachtell, Lipton, Rosen & Katz corporate partner David Katz, who last week represented the board of directors for Chesapeake Energy on its $5.38 billion sale of 435 natural gas and oil shale fields, is advising QEP on a deal expected to close by year’s end.