How di Standard Oil become an monopoly?

Standard Oil became a monopoly through aggressive business practices, including horizontal and vertical integration. By acquiring competitors and controlling various stages of oil production, refining, and distribution, it eliminated competition and achieved economies of scale. Additionally, John D. Rockefeller utilized secretive deals, rebates from railroads, and strategic pricing to undercut rivals. These tactics allowed Standard Oil to dominate the oil industry and significantly reduce competition by the early 20th century.