How many companies did Standard Oil monopolize?

Standard Oil, founded by John D. Rockefeller in 1870, effectively monopolized over 90% of the U.S. oil refining industry at its peak. The company controlled numerous subsidiaries and affiliated companies, which included major entities like the Ohio Oil Company, the National Transit Company, and the Atlantic Refining Company. Ultimately, Standard Oil's practices led to its dissolution in 1911 by the U.S. Supreme Court, which deemed it a violation of antitrust laws. The breakup resulted in the formation of 34 independent companies.