Approximately 90 per cent of the production of north and west-central Texas has come from the major positive structural elements: the Bend, Electra and Muenster arches. Increased attention is now being given the bordering basins, especially the north end of the Fort Worth syncline, in which five new fields were found during 1939.

In north Texas shallow reservoirs of Cisco age have contributed by far the greater part of the total production and proved reserves, but shallow production is now declining while deep production, especially from the Strawn, is of ever-increasing importance. Three 1939 discoveries in Archer, Clay, and Montague counties are producing from limestones of Bend age; previously no Bend production had been found north of Young County.

The reflection seismograph has had conspicuous success in the deeper parts of the east half of the north Texas district, but west of the Bend arch it has not yet demonstrated its application except in the discovery of two reef-like masses of Canyon limestone, one of which produces oil in the Seymour field, Baylor County. Surface mapping is no longer an important exploratory tool, but systematic subsurface work is of increasing importance.

Simpson sediments were encountered above the Ellenburger limestone near the axis of the Fort Worth syncline, and increased thickness of post-Ellenburger Ordovician may be looked for farther south in the deeper parts of the syncline.

The top of the Ellenburger was reached in Hardeman County at the greatest depth found to date west of the Muenster arch. The name Hardeman syncline is proposed for the large syncline lying between the Electra arch and the Wichita Mountains.