What was the core business that made Standard Oil a horizontally integrated monopoly?

Standard Oil Co. Inc. was an American oil producing, transporting, refining, and marketing company. Established in 1870 by John D. Rockefeller as a corporation in Ohio, it was the largest oil refiner in the world of its time. I'ts controversial history as 1 of the worlds 1st and largest multinational corporations ended in 1911, when the U. S. Supreme Court ruled that standard was an illegal monopoly.