Ex-Pioneer CEO Sheffield Joins Tamboran as Riddle Quits

Tamboran Resources Corp. said Monday Joel Riddle had resigned as chief executive and managing director and that chair Dick Stoneburner has stepped up as interim CEO.

“In addition to these changes, Mr Scott Sheffield and Mr Phillip Pace have been appointed as non-executive directors of Tamboran. As a result, Mr John Bell Sr has stepped down from Tamboran’s Board of Directors”, Tamboran, which develops unconventional gas resources in Australia’s Northern Territory, said in a regulatory filing.

Tamboran continues to have nine directors. It has started searching for a new CEO.

Sheffield founded and served as CEO of Pioneer Natural Resources Co. until December 2023. He remained at Pioneer as director until May 2024, when Exxon Mobil Corp. completed its acquisition of the company.

Investigation by the United States Federal Trade Commission under the Biden administration found last year that Sheffield had talks with OPEC+ officials about artificially controlling production. That led to the FTC banning Sheffield from holding a board or advisory position at the enlarged ExxonMobil as a condition in issuing a consent order for the combination.

Pioneer and Sheffield denied the accusation. However, Pioneer said at the time Sheffield would not contest the condition in order for the FTC to clear the merger.

On July 14, 2025, the FTC said it had denied Sheffield’s position to have the previous FTC’s consent order quashed.

“Sheffield’s petition to reopen and set aside the final order in its entirety must be denied because Sheffield is not a party to the final order and therefore cannot make use of the petition process, as defined by the FTC’s Rules of Practice, specifically Rule 2.51”, the FTC said.

However, three days later, the FTC canceled its consent order for the merger, along with the consent order for Chevron Corp’.s acquisition of Hess Corp., saying the previous FTC’s complaints about potential harm to competition were technically deficient.

“Exxon has already consented to setting aside the final order and has waived all its rights under rule 3.72(b). Today’s decision accordingly sets aside the final order without further process”, the FTC said July 17.

Notwithstanding, Sheffield told the press he no longer wanted to join ExxonMobil.

Fred Barrett, chair of Tamboran’s Nomination and Corporate Governance Committee, said Sheffield and Pace, an ex-director of Lonestar Resources US Inc. and a former managing director of Chambers Energy Management, “bring extensive leadership, operational, financial, capital raising, strategic partnering and risk management expertise to Tamboran”.

“Their perspectives will be invaluable as we continue to prioritize strategic execution and operational innovation to capitalize on the enormous potential of the Beetaloo Basin”, Barrett added.

“With the appointments of Scott and Phillip, the board has meaningfully deepened its expertise in large-scale shale development”.

In Australia, Sheffield also served as director of Santos Ltd. from 2014 to 2017.

On Riddle, Stoneburner, Tamboran’s interim CEO, said, “Since joining Tamboran as CEO in 2013, Mr Riddle has overseen the Company’s transformation from early-stage natural gas exploration to the brink of commercial production. Under his leadership, Tamboran has pioneered integrated development strategies that combine recognized U.S. shale techniques with Australian operations, driving significant productivity and efficiency gains”.

“Additionally, under Joel’s leadership, Tamboran successfully acquired and expanded its key assets and operations, resulting in the Company becoming the largest acreage holder and operator in the Beetaloo Basin, with approximately 1.9 million net prospective acres”, Stoneburner added.

“On behalf of the Board, I thank Joel for his dedicated service to Tamboran over the last 12 years and John for his valuable membership on our Board”.

To contact the author, email jov.onsat@rigzone.com