Answer: Buying rival refineries
Explanation: American industrialist John D. Rockefeller was born July 8, 1839, in Richford, New York. He built his first oil refinery near Cleveland and in 1870 incorporated the Standard Oil Company. By 1882 he had a near-monopoly of the oil business in the U.S., but his business practices led to the passing of antitrust laws.
Standard Oil gained a monopoly in the oil industry by buying rival refineries and developing companies for distributing and marketing its products around the globe.