A petrographic examination was made of approximately 450 thin sections prepared from the Spraberry formation of the Midland basin, West Texas, and, from the examination, a genetic sequence has been developed. This sequence is divided into two major stages and several substages. Later processes, occurring during the epigenetic stage, were the most important in the development of the section into an economic reservoir.

The Spraberry formation is traced throughout the Midland basin and divided into two units, the upper and lower. Isopach, clastic ratio, sand-isopach, and texture maps have been constructed to show the changes of the sedimentary attributes throughout the Midland basin and interpret the depositional history of the rocks.

The Midland basin was a restricted intracratonic basin during Spraberry time. All the data indicate a source of sediments on the north or northwest. South of the major area of production the sand and silt were too poorly developed to form favorable reservoirs. On the north, not enough favorable shale was deposited for the formation of large volumes of petroleum.