One of President Roosevelt's largest trust-busting cases came against John D. Rockefeller's Standard Oil Company, which controlled 91% of oil production in 1904. After concluding in 1906 that Standard Oil had created a monopoly, Roosevelt's administration filed an antitrust case, which ended in 1911 when federal judges ordered the company broken up.
Standard Oil Plant of Whiting, Indiana, 1910. Photograph by W. H. Wiseman. Prints and Photographs Division, Library of Congress.