ONEOK, Inc. is a diversified Fortune 200 corporation based in Tulsa, Oklahoma. ONEOK was founded in 1906 as Oklahoma Natural Gas Company, but It changed its corporate name to ONEOK in December 1980. It also owns major natural gas liquids (NGL) systems due to the 2005 acquisition of Koch Industries natural gas businesses.

ONEOK's Energy Services operation focuses primarily on marketing natural gas and related services throughout the U.S. Energy Services, which derives more than 84 percent of its earnings from the physical marketing business, showed an operating income increase of $26.5 million. Energy Services’ retail business participates in customer gas choice program in Nebraska and Wyoming.

On December 22, 2005, The ONEOK Foundation said it would donate $1 million this winter to assist residents in Oklahoma, Kansas and Texas with their energy bills.

In 2007, Fortune magazine named ONEOK the most admired company in the energy industry.

ONEOK's predecessor, Oklahoma Natural Gas Company (ONG), had been headquartered in an Art Deco building on the northwest corner of Seventh Street and Boston Avenue in Tulsa since 1928. In 1982, ONEOK chairman, J. E. Tyree, announced plans to demolish the ONG building and replace it with a new 16-story tower. However, this did not happen. Instead, ONEOK bought the Cities Service Company (later renamed Citgo) in August, 1982. The acquired company already had a project underway to build a high-rise headquarters building at Fifth and Boulder. ONEOK realized that it would be more economical to cap the planned structure at 17 stories and move its headquarters there, rather than to proceed with its original plan. It completed the new black granite and glass tower in 1984.

In 2009, ONEOK sponsored the construction of ONEOK Field, the new Tulsa Drillers minor league baseball stadium in downtown Tulsa.

Oklahoma Natural Gas Company (ONG) was founded in 1906 by two attorneys, Dennis T. Flynn and Charles B. Ames, who planned to develop the natural gas that was a byproduct of the northern Oklahoma oilfields. ONG incorporated on October 9, 1906, under the laws of Oklahoma Territory. Flynn was president and Ames the secretary. Joined by Chicago entrepreneur, H. M. Byllesby, for whom they worked, they also formed the Oklahoma Gas and Electric Company (OG&E) to bring natural gas from the Cleveland Oil Field to Oklahoma City, using it to generate electric power. Byllesby soon resigned, but Glenn T. Braden and Theodore N. Barnsdall joined ONG. Both were already experienced oilmen. Together, they owned the Osage and Oklahoma Gas Company. Braden had been an executive of Standard Oil Company and Barnsdall an oil producer. ONG built a natural gas pipeline from the Osage fields to Oklahoma City which went into service December 28, 1907. ONG extended the line to Guthrie and Shawnee. It also built the first gas pipeline compressor station in the state in 1910. Braden followed Flynn as president of the company.

ONG continued to build pipelines throughout Oklahoma. By the time Braden retired in 1921, ONG owned over 1,300 miles (2,100 km) of lines and served over a half million customers in 48 of the state's 77 counties. In 1928, it built its noted headquarters building in Tulsa. It reorganized several times, first becoming a Maryland Corporation, then a Delaware Corporation.

The board of directors voted to change the name of Oklahoma Natural Gas Company to ONEOK, Inc. in December 1980. The part of the corporation that operated utility services became a separate division named Oklahoma Natural Gas and headquartered in Oklahoma City. The parent company is headquartered in Tulsa.

In February 2014, ONEOK spun off its natural gas distribution companies (Oklahoma Natural Gas, Kansas Gas Services, and Texas Gas Services) into a separate publicly traded company, ONE Gas.

Oklahoma Natural Gas, the company that started it all back in 1906, now operates as a division of ONE Gas.