In 1891 members of an enterprise called the Utah Oil Company, whose incorporators included Simon Bamberger and C.J. Millis, sank a shallow well near the town of Green River, Utah. Not finding any oil, the company abandoned its well after drilling to a depth of 1,000 feet. During the remainder of the 1890s, oil and gas prospectors sank approximately twenty-five wells in various parts of the state.

By mid-1907 Washington and San Juan counties in southern Utah had become the focal points of oil-field activities. Early in that year Pat Holohan, a Nevada miner, found outcroppings of oil sand near a settlement called Virgin City in Washington County and quickly drilled two wells. Twelve different companies soon put down fourteen wells in the region. At the same time, a former gold prospector named L.L. Goodridge began drilling a well at Mexican Hat on the San Juan River in San Juan County. In March 1908 Goodridge produced a gusher, and by the end of 1909 as many as seven oil companies had started work on no less than twenty-five wells around Mexican Hat. While neither Virgin City nor Mexican Hat ever became major oil-producing fields, enough oil was extracted from both to supply small local refineries that operated intermittently for many years.

However, the prospect of finding petroleum continued to lure a few explorers to various regions of Utah, and from 1916 to 1921 several companies, including such major operators as the Ohio Oil Company and the Midwest Refining Company, drilled a dozen deep test holes. Observing the persistence of these enterprises, one writer concluded in 1925 that their efforts were justified because Utah's structural and surface conditions held "exceptional promise for oil and gas accumulation."

During the 1920s Earl Douglas, a paleontologist who discovered fossils in the area that became Dinosaur National Monument, was an eloquent spokesman for Utah's oil industry. Being interested in petroleum geology and having conducted many scientific investigations in the Uinta Basin, Douglas became convinced that that region contained a great deal of oil, and throughout the 1920s he called attention to the Uinta Basin by writing journal articles and letters of correspondence, and by visiting financial centers to seek support for drilling projects.

Utah's oil industry managed to survive the slowdown. Developers continued to drill in Washington County's Virgin oil field and completed a total of sixty wells before 1944. Standard Oil of California sank two test holes in Emery County, and the Utah-Southern Oil Company remained active in Grand County, even drilling one well to a depth of 6,715 feet. William E. Nevills, who began to work in the Mexican Hat oil field in the mid-1920s, enlarged his operations by adding three wells to his string of small producing wells.

Toward the end of World War II oil men began to accelerate Utah's petroleum operations once again. This time they succeeded to the extent that from 1945 through 1947 they finished the groundwork necessary to propel the state into a period of commercial oil production. The focal point of these activities was the Uinta Basin. Here a number of large companies such as Standard Oil of California, Pure, Continental, Gulf, Carter, and Union began to explore more seriously than at any time previously. Despite the presence of these major firms, however, the Equity Oil Company, a Utah-based enterprise under the leadership of J.L. Dougan, was the first to find commercial amounts of oil in the Uinta Basin. Dougan was drilling in Ashley Valley on 18 September 1948 when his company tapped a pool of oil that produced 300 barrels a day. Within the next seven years, major oil companies would open Uinta Basin fields, including Roosevelt (1949), Red Wash (1951), Walker Hollow (1953), and Bluebell (1955). These fields became part of two giant oil-producing complexes--Greater Altamont/Bluebell and Greater Red Wash--which ultimately included White River (1961), Cedar Rim (1969), and Altamont (1970).

From the late 1940s until 1975 almost all of Utah's oil development occurred in an area extending down the eastern border of the state from the Uinta Basin to the San Juan River. The one exception to this was the Upper Valley oil field, which is located ten miles southeast of Escalante in Garfield County. In 1964 Tenneco opened the Upper Valley field. By 1978 there were twenty-six active wells that were capable of producing a total of one million barrels of petroleum a year.

In the 140 years since Stansbury's first discovery, nearly one hundred sixty fields have been explored, and approximately 900,000,000 barrels of oil have been produced in Utah (Texas yielded almost that much petroleum in 1947). Utah's number of productive wells increased from 225 in 1957 to 875 in 1968 and 1,300 in 1978. While the state's contribution to the amount of oil produced in the United States has remained relatively minor, the petroleum industry has become one of Utah's significant commercial enterprises.

The future of Utah's petroleum industry may be found in the extensive oil-shale and tar-sand reserves located in the eastern half of the state. Utah's oil-shale reserves are estimated at several trillion barrels, with the richest deposits located in the Uinta Basin, where 90 to 115 billion barrels are contained in deposits that have the potential to yield twenty-five or more gallons per ton. Tar-sand, or oil-impregnated rock, is located in more than fifty deposits stretching from the Uinta Basin south into San Juan and Garfield counties. Utah's tar-sand deposits contain an estimated 23 to 29 billion barrels. Beginning in 1970, the United States Department of the Interior started several programs to stimulate oil-shale and tar-sand development; however, commercial extraction of petroleum from oil-shale and tar-sand at this time remains a potential rather than a reality.