Final answer:
John D. Rockefeller and businessmen like him sold oil after refining it. Standard Oil, led by Rockefeller, achieved nearly complete control over the oil industry through horizontal and vertical integration strategies. By the 1890s, Standard Oil dominated 90 percent of U.S. refineries.
Step-by-step explanation:
According to John D. Rockefeller's business practices, businessmen, including Rockefeller himself, sold oil after refining it. Through his company, Standard Oil, Rockefeller engaged in horizontal integration, merging with other oil companies or driving them out by underpricing his product. He established trusts to control other oil companies, essentially creating a monopoly in the oil industry. Determined to dominate, Rockefeller had his trustees buy out competitors, often after engaging in price wars that damaged his competition's ability to remain viable. After gaining substantial control, he would raise oil prices significantly.
Moreover, Rockefeller practiced vertical integration by controlling every aspect of the product's lifecycle, which allowed him to further drive competitors from the market. By the 1890s, his aggressive and strategic business moves led to Standard Oil controlling 90 percent of the nation's oil refineries, effectively making it the most powerful entity in the U.S. oil industry. These tactics by Rockefeller and other industrialists led to the establishment of corporate dominance in various industries across the United States during this period.