Sundance Square, among downtown Fort Worth’s largest property owners, has added the Petroleum Building to its portfolio following the recent purchase of the building from XTO Energy.

XTO Energy, an oil and gas subsidiary of ExxonMobil, will lease back the building through July, but it has the option to extend that lease for an additional year, according to deed records.

Sundance Square did not say what its plans are for the 14-story office building once XTO moves out.

“The availability of the Petroleum Building presented a great opportunity to bring the landmark building into our portfolio,” Johnny Campbell, Sundance Square CEO, said in a statement released Monday.

The sale comes six months after XTO put the office building and an adjoining 534-space parking garage on the block. The property takes up a full city block between Fifth and Sixth streets and Houston and Throckmorton streets. The parking garage eventually will be incorporated into Sundance Square’s free parking program for guests, it said.

With the addition of the Petroleum Building, Sundance Square said it has about 4 million square feet of office, retail, and residential in 44 buildings.

The sale closed Jan. 19, deed records show. A sales price was not disclosed. The Tarrant Appraisal District appraises the property at about $9 million.

Sundance Square bought the building under the entity Sundance Parliament of Owls, Llc., part of Fine Line Diversified Realty Inc., a real estate arm of billionaire businessman Ed Bass, deed records show.

Sundance Square encompasses 35 blocks, some with historic buildings it redeveloped for shops, restaurants, offices and residences. It’s also built several office buildings, but is known for its signature office buildings, the 33-story Well Fargo Tower at Second and Main, and the 38-story Bank of America Tower at Third and Commerce.

More recently, Sundance Square built The Carnegie at Third and Taylor streets, and The Commerce Building and The Westbrook, which bookend Sundance Square Plaza, and The Cassidy at Third and Houston streets.

This is the first property Sundance Square has bought in downtown since 2010, when it acquired a 15,000-square-foot parcel at the southwest corner of Third and Commerce, which gave it the land needed to complete its 1-acre outdoor plaza.

In June, XTO Energy announced it was pulling the majority of its Barnett Shale operations out of downtown Fort Worth and moving them to Houston. About 1,600 employees will leave downtown by 2020, but about 350 employees will stay.

JLL Executive Vice President Ryan Matthews represented XTO Energy in the transaction.

“We’re very proud of the outcome,” Matthews said in a statement. “XTO hoped to secure a buyer who understood the level importance the Petroleum Building has for downtown Fort Worth. Sundance Square obviously fits this profile. We know that this historic asset is in great hands.”