Fractured pre-Cambrian basement rocks are the reservoir from which over a million barrels of oil have been produced from sixteen wells in the Orth field, Rice County, Kansas. Similar fractured quartzite is the reservoir from which oil has been produced in four wells in the Kraft-Prusa field and from one well each in the Beaver, Bloomer, Eveleigh, and Trapp fields, all in Barton County; and from six wells in the Ringwald field, five wells in the Heinz field, and two wells in the Silica field, all in Rice County. Fresh pink biotite granite is the reservoir rock producing oil in three wells in the Hall-Gurney field and in one well in the Gorham field, both in Russel County. A few other wells, not investigated by the writer, are reported to be producing from pre-Cambrian rock .

All wells known to be producing from pre-Cambrian quartzites are on the summits of buried pre-Cambrian hills. Porosity consists of a reticulated fracture system. The pre-Cambrian reservoir rocks are unconformable overlapped by Pennsylvanian limestones draped above the hills in gentle anticlinal folds which trap oil in multiple thin porous zones in the Topeka (Virgil) and Lansing-Kansas City (Missouri) limestones. Oil migrated locally into the fractures in the pre-Cambrian rocks from the overlying Pennsylvanian rocks or from the truncated Cambro-Ordovician Arbuckle dolomites, themselves an oil reservoir, which are on the flanks of each hill.

It is the writer's opinion that the basement rocks have been inadequately tested in the past. Where encountered structurally (or topographically) high, the fractured pre-Cambrian basement rocks are worthy of careful consideration as a potential commercial oil reservoir.