The Pew brothers' old Sun Oil Co. was an empire that built tanker fleets, sent engineers to Arctic and tropical fields, picked and financed Republican candidates, and ran steaming refineries from the Delaware and Schuylkill to West Africa and East Texas. It all happened from paneled offices atop 1608 Walnut St., later in Radnor and at 1818 Market.

But pieces of the empire have continued to leave town since Dallas investor Kelcy Warren's Energy Transfer Partners (ETP) bought control of the company's former retail and pipeline units in 2012.

Robert W. Owens, chief executive of Sunoco L.P., the gas-station and convenience-store group that operates more than 850 locations and supplies thousands more, is moving with his senior staff from offices at Ellis Preserve in Newtown Square to Dallas, local employees told me.

Another Sun Oil successor, Sunoco Logistics Partners L.P., the pipeline and transport company that operates the Marcus Hook Industrial Complex storage and export facilities and the Mariner pipeline projects, closed the last of its Philadelphia offices last fall and is now based at the Newtown Square center.

Sunoco Logistics, however, also operates the Fort Mifflin terminal on the Delaware. The company's employment in all of Pennsylvania is about 600, up from 400 in 2010, thanks to the revival of Pennsylvania gas industries.

Sunoco L.P.'s move to Texas "allows some of our core corporate functions to operate from a region central to our expanding geographic footprint, and also close to our parent company's headquarters," said spokesman Jeff Shields in confirming the moves.

The company plans to "grow significantly" from its new Texas home, he added.

Besides Owens, "some of his senior staff and designated team members from various corporate functions" are being invited to move west if they want to stay with the company, Shields said.

The move follows more acquisitions by Sunoco L.P. since its 2014 combination with Texas-based Susser Holdings Corp., which operates Stripes stores and stations in the Southwest. ETP picked the Sunoco name for the combined, publicly traded stores group.

Before going to Texas, Sunoco L.P. had consolidated staff from Philadelphia and Lester, Delaware County, to the Newtown Square site, in 2013.

The Sunoco center was set up for 700 employees, says Stephen M. Spaeder, senior vice president at Equus Capital Partners Ltd., which developed the former girls' school property north of the SAP America Inc. complex on West Chester Pike.

About 450 Sunoco L.P. people now work there, plus an additional 100 for Sunoco Logistics, spokesman Shields told me.

Sunoco L.P. also plans to close an office in suburban Reading, Berks County, "in 2016 or 2017," Shields said. "Some of the approximately 35 positions there are being transferred to Dallas, with others moving to the field."

The moves aren't over: Although "we expect to maintain a significant presence in Newtown Square" - and in Corpus Christi and Houston, where Susser was based - "we will be asking some employees in these offices to relocate," Shields added.

Sunoco L.P. is "still working on the exact numbers" who will remain in the Philadelphia area, he said. Shields promised Sunoco L.P. would continue "its commitment to the Delaware Valley" and its markets.

Besides Stripes and Sunoco's APlus mini-mart and pumping stations, Sunoco L.P. has acquired Circle K stores in the Northeast, Quick Stop and Laredo Taco stores in the Southwest, and Aloha markets in Hawaii, among its properties.