ExxonMobil Corp.’s board was scheduled to meet to elect a new CEO and chairman after Rex W. Tillerson on Tuesday officially was nominated by President-elect Trump to serve as secretary of state.

Tillerson, a dark horse candidate, is said to have become the top choice at the urging of establishment Republican leaders including Dick Cheney, James A. Baker III and Condoleezza Rice.

“His tenacity, broad experience and deep understanding of geopolitics make him an excellent choice for secretary of state,” Trump said. “Rex knows how to manage a global enterprise, which is crucial to running a successful State Department, and his relationships with leaders all over the world are second to none.”

Tillerson, who has never held public office, said he shared Trump’s vision for “restoring the credibility of the United States’ foreign relations,” and he vowed to “focus on strengthening our alliances, pursuing shared national interests and enhancing the strength, security and sovereignty of the United States.”

ExxonMobil’s Suzanne McCarron, vice president of public and government affairs, said the board congratulated Tillerson on the nomination and was planning to meet “shortly regarding transition.”

As of late Tuesday afternoon, ExxonMobil had not made any announcements about who would succeed Tillerson. However, the management team at the No. 1 natural gas producer in the country is deep, with several top lieutenants able to step into the CEO role.

Wichita-native Darren W. Woods, 51, who is rumored to be at the top of the list to take over, joined Exxon Company International in 1992 as a planning analyst and in 2005 became vice president of ExxonMobil Chemical Co. He was appointed vice president of the corporation in 2012 and named senior vice president (SVP) in 2014. Early this year he was elected president and appointed to the board, which was Tillerson’s position before he was promoted in 2006.

Also within the top executive ranks is principal financial officer Andrew P. Swiger, who joined the company in 1978 as an operations engineer and was named executive vice president (EVP) of ExxonMobil Production Co. in 2004. He was promoted to president of ExxonMobil Gas & Power Marketing in 2006 and named SVP of the corporation in 2009.

Other executives on the short list include SVP Michael J. Dolan, who joined Mobil Oil Corp. in 1980 and was promoted to the worldwide petrochemicals division in 1993. He became president in 2004 of ExxonMobil Chemical and in 2008 was appointed SVP of the corporation.

SVP Jack P. Williams, an Ohio native, joined Exxon in April 1987 as a drilling engineer. In 2010 he was named president of ExxonMobil’s North American onshore subsidiary XTO Energy Inc. and in 2013 was named EVP of the production unit. Two years ago he was elected as SVP. And Mark W. Albers, a Calgary native, joined the company in 1979. He became president of ExxonMobil Development Co. in October 2004 and elected SVP of the corporation in April 2007.

The Trump transition team, which may face pushback during the Senate confirmation hearings, was lining up endorsements for Tillerson.

Robert M. Gates, who served as secretary of defense under President Obama and President George W. Bush, called Tillerson “a global champion of the best values of our country” and said he would bring “vast knowledge, experience and success in dealing with dozens of governments and leaders in every corner of the world.”

Sen. Bob Corker (R-TN), who would oversee confirmation hearings as chairman of the Senate Foreign Relations Committee, called Tillerson “a very impressive individual and has an extraordinary working knowledge of the world. I congratulate him on his nomination and look forward to meeting with him and chairing his confirmation hearing.”

Some of Tillerson’s stated positions, given in policy speeches for years, are at odds with the president-elect. Tillerson has said, for instance, that he believes humans are affecting the climate through greenhouse gas emissions, while Trump has said the issue remains up for debate.

And while Trump has called President Obama’s signature Trans-Pacific Partnership (TPP) a “potential disaster,” the ExxonMobil chief in 2013 said in a speech to the Global Security Forum that the TPP was “one of the most promising developments” for the country’s businesses.

“The 11 nations that have been working to lower trade barriers and end protectionist policies under this partnership are a diverse mix of developed and developing economies,” Tillerson said. “But all of them understand the value of open markets to growth and progress for every nation.”

In 2007, before the Council on Foreign Relations, Tillerson also warned about the United States becoming insulated from the “impact of world events on the economy” as unconventional gas and oil production moved the country toward energy independence.

“Like the Council’s founders, I believe we must choose the course of greater international engagement,” Tillerson said. “The central reality is this: The global free market for energy provides the most effective means of achieving U.S. energy security by promoting resource development, enabling diversification, multiplying our supply channels, encouraging efficiency, and spurring innovation.”

Republican senators would hold a 52-48 majority in the next Congress, a thin margin to ensure Tillerson’s confirmation if any defected and sided with Democrats to block the appointment.

Arizona Republican Sen. Jeff Flake, who sits on the Foreign Relations Committee, the first to approve a nominee before a floor vote, said the support for Tillerson from Gates and others “carry considerable weight.”

Sen. Marco Rubio (R-FL), who also sits on the Foreign Relations Committee, said he had “serious concerns” about the nomination. He called Tillerson was a “respected businessman” but questioned whether he was the right person for the position.

“The next secretary of state must be someone who views the world with moral clarity, is free of potential conflicts of interest, has a clear sense of America’s interests, and will be a forceful advocate for America’s foreign policy goals to the president, within the administration, and on the world stage,” Rubio said.

The Florida senator promised to do his “part to ensure he receives a full and fair but also thorough hearing…”

GOP Sens. John McCain of Arizona and South Carolina’s Lindsey Graham also are raising concerns about ExxonMobil’s business deals with Russia, but they have not said publicly they would vote against Trump’s nominee.

Incoming White House Chief of Staff Reince Priebus told reporters Tuesday the choice had come down to chemistry between Trump and Tillerson. He also rejected the idea that Tillerson’s longstanding business relationships with Russia would be disqualifying.

The Obama administration in 2014 had joined the European Union in imposing sanctions against Russia for military intervention in Ukraine. The U.S. Department of Treasury also issued stringent sanctions, targeting firms operating in Russia’s energy sector. Under the Treasury sanctions, U.S. companies were required to shut down operations with Russian partners.

Even though Tillerson criticized the sanctions, Priebus said the ExxonMobil chief believed they were an important part of diplomacy if they are adequately enforced. “He’s not against sanctions,” Priebus said on MSNBC’s “Morning Joe” program Tuesday.

However, during the May 2014 ExxonMobil shareholder meeting, which followed the U.S. sanctions against Russia, Tillerson said, “We do not support sanctions, generally, because we don’t find them to be effective unless they are very well implemented comprehensively, and that’s a very hard thing to do.”