Drilling for oil in Ohio began in 1860. Drillers opened the first oil well in Ohio history near Macksburg, in Washington County. Additional wells soon appeared in Washington County and Noble County as well. By 1950, various companies had drilled more than 175,000 wells in forty-five Ohio counties. These wells had produced approximately 615 millions of oil. Most of Ohio's oil reserves are located in northwestern and eastern parts of the state, with the largest concentrations being located south of Toledo. As of 1950, oil companies guessed that the equivalent of another twenty-eight million barrels of oil remained under Ohio's surface.
During the late nineteenth century and the early twentieth century, numerous Ohio companies amassed fortunes from the oil industry. The Standard Oil Company came to dominate oil refining during this era, having a virtual monopoly. As the federal government sought to prohibit monopolies during the late 1800s and the early 1900s, Standard Oil lost its stranglehold over the industry. By the start of the twentieth century, oil drilling in the United States had shifted from states like Ohio to locations in the American Southwest. Ohio companies also moved westward. The Ohio Oil Company began to drill for oil in the Rocky Mountains during the early 1900s, although it also continued to extract oil from Ohio's soil. At the start of the twenty-first century, Ohio still produces some oil. In 1981, more than six thousand new wells appeared in the state, although companies drilled fewer than seven hundred new wells in 1993.