The Spraberry-Dean Sandstone fields consist of many tongue-shaped, oil-producing areas in the Midland Basin, a province of the Permian Basin of West Texas. The most prolific fields are located in Borden, Dawson, Glasscock, Martin, Midland, Reagan, Sterling, Tom Green, and Upton counties. The fields produce from sands that are divided into three genetic sequences of Permian age-upper Spraberry, lower Spraberry, and Dean. The sands are found in a submarine fan system that covers the entire Midland Basin. Oil is trapped by updip pinchouts and facies changes at depths of 5,100 to 8,300 feet. The sands are closely packed and tightly cemented, giving low porosity and allowing an average recovery efficiency of only 15 percent. The expectation of a low recovery efficiency led many explorationists to call the sands the largest uneconomic oil-producing pay in the world. The seven largest-volume fields of the play are Ackerly, Benedum, Calvin, Cope, Jo-Mill, Pegasus, and Spraberry Trend. Spraberry-Dean fields are significant because their estimated reserves in original place were more than 10 billion barrels of oil. The first recognition of the Spraberry sand as an oil producer came in 1944, when Seaboard Oil Company drilled a dry hole on the Abner J. Spraberry farm in east central Dawson County. In the well samples a sandstone, locally called Spraberry, showed traces of oil. Little attention was given to its potential as a producing formation and no attempts were made to complete the Seaboard No. 1 Spraberry in the sandstone. However, in January 1949 another well, the Seaboard No. 2-D Lee, was completed in the upper Spraberry at a depth of 6,420 to 6,700 feet. Although the well tested a flowing potential of 319 barrels of oil a day on January 22, 1949, it attracted little interest. The second discovery came a month later on February 24 in the Tex-Harvey Oil Company No. 1–16 Floyd, located in east central Midland County sixty-five miles south of the No. 2-D Lee. The No. 1–16 Floyd was completed at a depth of 7,865 to 7,875 feet in the lower Spraberry with a pumping potential of 135 barrels of oil a day. It was the discovery well for Tex-Harvey field, but it created no more interest than did the Seaboard No. 2-D Lee.
Although the first two Spraberry wells gained little attention, explorationists soon learned that the Spraberry-Dean sands existed in all areas of the Midland Basin and that wells drilled to that objective were never dry holes. Confident in the knowledge that every well was a potential producer, operators set off a drilling frenzy in 1950 and 1951. Two new Upton County fields were opened early in 1950. On January 8 the Humble Oil and Refining Company (later Exxon Company, U.S.A.) No. 1 Pembrook was completed in the northeastern part of the county to a depth of 7,030 to 7,100 feet in the upper Spraberry with a daily pumping potential of thirty-four barrels of oil. The No. 1 Pembrook was the first producer in Pembrook field. On April 3 the Republic Natural Gas Company No. 1 Barnett, located at the north end of the Benedum pool in east central Upton County, was brought in at a depth of 7,500 to 7,540 feet in the lower Spraberry and pumped thirty-three barrels of oil a day. This was the discovery well in Benedum Spraberry field, which reported a cumulative yield in excess of 24 million barrels of oil by 1994. Spraberry-Dean excitement dominated Midland Basin drilling throughout the remainder of 1950 and into 1951 with field extensions and new field discoveries. On November 12, 1950, Tex-Harvey field was expanded to the east into Glasscock County by the completion of the Russell Wrage No. 1–20 Hendrickson, which flowed 184 barrels of oil a day from 6,910 to 7,175 feet in the upper Spraberry. A six-mile southern extension was added to Tex-Harvey pool by the Ted Weiner No. 1–16 Driver, brought in on January 26 at a depth of 7,110 to 7,325 feet in upper Spraberry for an initial flowing production of 303 barrels of oil a day. The Honolulu No. 1-A Suggs was completed on December 15, 1951, in Sterling County to a depth of 5,151 feet in the upper Spraberry for an initial production of 349 barrels of oil a day. It was the discovery well in Cope field, which eventually extended into Tom Green and Reagan counties. In 1960 a water flood boosted production in the field and by 1994 cumulative production in Cope field surpassed 12.3 million barrels of oil.
By early 1952 Spraberry-Dean drilling peaked in the Midland Basin as one new field was found early in the year. On January 10, 1952, the Republic No. 2 American Republics Corporation encountered oil at 4,897 feet in southwestern Midland and northwestern Upton counties. It was the discovery well in Pegasus Spraberry field, which reached a cumulative yield of more than 14.5 million barrels of oil by 1994. On May 1, 1952 the Midland Basin reported 1,630 producing wells, but operators began to look realistically at Spraberry-Dean drilling. It was obvious that a guaranteed producing horizon did not necessarily guarantee economic success. With the average well costing $125,000 to drill, the average well producing 50 barrels a day, and crude selling for an average price of $2.51 per barrel, payout was a distant goal. When many Spraberry-Dean wells failed to make their allowables, interest waned among explorationists. On March 1, 1953 the Railroad Commission of Texas combined several small fields into a pool named Spraberry Trend. Among the consolidated fields were Aldwell, Germania, Midkiff, Pembrook, Spraberry, and Tex-Harvey. Spraberry Trend became the largest producing area among Spraberry-Dean fields, eventually covering 500,000 acres of land around the common corners of Midland, Glasscock, Reagan, and Upton counties. Operators in the Spraberry Trend actively produced oil, but they also brought up large volumes of casinghead gas for which they either found no outlet or deemed worthless. Because it was impossible to bring up crude without producing casinghead gas, operators flared an estimated 220 million cubic feet of gas each day until March 25, 1953. On that day the Railroad Commission shut in more than 1,800 wells in Spraberry Trend that were connected to gasoline plants that flared residual gas or were not connected to those plants and flared gas on their own. After nine months operators convinced the Railroad Commission that flaring had stopped in the field, and production was resumed in January 1954. In the 1960s and 1970s other fields were added to Spraberry Trend. They were Playa, Stiles, Billington, and North Sugg fields. By 1994 Spraberry Trend reported a combined cumulative total of nearly 692 million barrels of oil.
In the first half of 1954 two additional Spraberry-Dean fields were found in the Midland Basin. On February 7, 1954, the J. E. Jones Drilling Company No. 2 W. L. Miller was completed in the lower Spraberry of southwestern Borden County to a depth of 7,452 feet for an initial production of 348 barrels of oil a day. The No. 2 Miller opened Jo Mill Spraberry field. By 1994 the field reached a cumulative total of more than 81.2 million barrels of oil. The second field was introduced on June 29, 1954, when the Stanolind Oil and Gas Company No. A-1 J. Y. Graves R/A "A" pumped 13 barrels of oil a day for its initial production. The No. A-1 Graves was located in the southeastern corner of Dawson County and found oil in Dean sands at a depth of 8,172 feet. It ushered in the Ackerly Dean field. By 1994 the Ackerly Dean and Spraberry fields reported a combined cumulative production in excess of 46.5 million barrels of oil. At the end of the 1950s and into the 1960s enhanced recovery projects began in Spraberry-Dean fields. Primary recovery in the fields had been driven by solution gas, but by 1959 unitization was initiated in leases of forty to 160 acres and water flood and water injection began. Production increased and explorationists again turned their attention to Spraberry-Dean drilling. Another important field was found. On November 17, 1965 Calvin field, producing from Dean sands, was opened in north central Reagan and south central Glasscock counties. By 1994 Calvin Dean field had brought up more than 44.4 million barrels of oil.
At the end of the 1970s and into the early 1980s, when the oil and gas industry experienced its greatest-ever boom and crude prices soared, Spraberry-Dean fields and their guaranteed producing wells flourished. In 1981 the seven most prolific Spraberry-Dean fields reported a combined cumulative production of 615.3 million barrels of oil, but over the next decade yields dramatically increased. With the advent of $32-per-barrel oil and the use of enhanced recovery, Spraberry-Dean wells became undeniable economic successes. Drilling with Spraberry and Dean objectives continued into the 1990s even when crude sold for half the boom price. By 1994 the combined cumulative total for the seven important Spraberry-Dean fields neared 924.4 million barrels of oil. The Spraberry-Dean zones of the Midland Basin, once called the largest uneconomic oil-producing pay in the world, approached the status of a billion-barrel area.