Donald Trump is expected to nominate Exxon Mobil CEO Rex Tillerson as his secretary of state, two sources close to the transition process told NBC News on Saturday.

Tillerson, 64, became president of the Texas-based oil company in 2004 and has a close business relationship with Russian President Vladimir Putin. He has spent his entire career at the company now known as Exxon Mobil.

The sources cautioned that nothing is final until the president-elect officially announces it, likely next week.

Tweet from Trump spokesman

The selection of Tillerson comes after Trump and his transition team spent weeks searching for someone to fill the post of the top U.S. diplomat. Former Republican presidential candidate Mitt Romney and former New York City Mayor Rudy Giuliani were reportedly in the running. Giuliani said Friday he had taken his name out of consideration.

Tillerson will be paired with former U.N. Ambassador John Bolton as his deputy secretary of state for day-to-day management of the department, one source added.

As secretary of state, Tillerson would be fourth in line to the presidency.

Other facts about Tillerson:

As of his latest SEC ownership filing update on Dec. 2, Rex Tillerson currently owns exactly $233,078,184 worth of Exxon Mobil stock, based on Friday's $89.00 closing price. (The exact number of shares he owns is 2,618,856).

Exxon Mobil is currently the fifth largest publicly-traded company in the entire world. The only companies ranking ahead of XOM and its $369,055,665,000 market value are Apple, Alphabet, Microsoft, and Berkshire Hathaway.

Tillerson has never worked anywhere other than Exxon. He joined the company after graduating college in 1975 to become a "production engineer", per his official Exxon bio

Additional reporting by CNBC staff.