Grayson County is located in the eastern part of north-central Texas, adjacent to the Red River. Sherman, the county seat, is about 70 miles north of Dallas.

Although occasional wildcat wells had been drilled in the county since early in the century, the first commercial oil pool, the Handy field, was not discovered until 1946. Development has been active since that time, particularly since the discovery of Oil Creek production in the Sandusky field in 1950. As a result, 15 oil fields with about 65 different pay zones have been discovered.

The main regional geological features are--Muenster arch, Marietta basin and associated Gordonville trough, and Ouachita facies of the eastern portion of the county. The Gordonville trough in the northwest portion of the county extends in a northwest-southeast direction paralleling the Muenster arch, and conforming generally to the structural grain established by the Wichita and Arbuckle orogenies in southern Oklahoma. The Sandusky platform, on which a substantial portion of the production in Grayson County is located, borders the Gordonville trough on the southwest, and owes its existence to a series of tremendous faults stepping down into the trough. In the southwestern quarter of Grayson County the Ordovician (Ellenburger) beds dip northeastward away from the crest of the Muenster rch, which lies further southwestward in northern Denton and southern Cooke counties. The geologic structure of the area is strongly influenced by faults, the major ones associated with subsidence of the Marietta basin and the minor ones connected with more local adjustments. The Sherman anticline is the largest anticlinal feature in the county, being about 12 miles long and having approximately 2,000 feet of closure.

The stratigraphic column includes beds from Gulf and Comanchean rocks at the surface down to probable Cambrian--possibly as much as 35,000 feet of sediments in the Gordonville trough. Cretaceous rocks rest on Pennsylvanian from Virgilian to Morrowan with great angular unconformity. Pennsylvanian from Deese down to lower Dornick Hills (or possibly Springer) rests with great angular and erosional unconformity on Mississippian (Woodford) down to Ordovician Ellenburger.

Most of the oil is found in sands of Desmoinesian age--Deese (Strawn)--upper Dornick Hills; Atokan--middle Dornick Hills; and Simpson (Ordovician)--Oil Creek sand.

Four oil fields, Handy, Sandusky, Big Mineral, and Sherman, are briefly described as examples of structure, stratigraphy, accumulation, and character of the production in the area.