John D. Rockefeller became the first billionaire in the United States by establishing and focusing on his oil refining business and monopolizing competition, explains Investopedia. Oil extraction in Montana and North Dakota paved the way for Harold Hamm to accumulate his wealth, while Philip Anschutz achieved his billionaire status by venturing into the oil and gas industry after he bought out Circle A Drilling, which was his father's drilling firm, in 1961, reports TheRichest.
Rockefeller was notorious for monopolizing the oil industry using techniques such as buying out competitors' companies and purchasing all oil barrels to cause a shortage, thus forcing unwilling firms to sell out, notes Investopedia. Nonetheless, he was the harbinger for research and development, which promoted more efficient processes and led to the creation of various important products used in different industries.
After taking over Kaiser-Francis Oil, George Kaiser transformed the company into one of the biggest nonpublic energy exploration firms in the United States and turned himself into a reputable billionaire, states TheRichest. Ray Lee Hunt similarly took over his father's firm, but he accumulated massive wealth after finding a large oil site in Yemen and engaging in oil deals for the extraction and refinement of the newly discovered oil.
Jeffrey Hildebrand quit his job as a petroleum engineer and founded the Hilcorp Energy Company, according to TheRichest. He then sought partners to purchase lands teeming with oil, leading to his success as a billionaire.