Upper Devonian-Lower Mississippian Woodford-Chattanooga black shales are oil source beds throughout Oklahoma and much of western Arkansas. Diagenesis in the Woodford-Chattanooga source section proceeded through the following relative time sequence: (a) silicification, chiefly by recrystallization of radiolarians, which probably followed the reaction conversion of amorphous opal-A to opal-CT to chert; (b) dolomitization of deep-basin opal or chert and shallow-platform carbonate laminae; (c) tectonic faulting, folding, and associated fracturing and stylolitization predominantly associated with the late Paleozoic Arbuckle and Ouachita orogenesis; (d) late silicification and mineralization along fractures contemporaneous with (e) generation and expulsion of petroleum.

The principal expulsion mechanism for these Upper Devonian-Lower Mississippian oil source rocks is whole-oil migration through coarser grained matrix pores, stylolites, and fractures, rather than diffusion on a molecular scale. Diffusion migration does occur but appears only to affect internal migration over a few millimeters within the source rock, and thus cannot account for expulsion of large volumes of oil. Preliminary calculations based on source rock extract data indicate that approximately 147 billion bbl of oil have been generated within Woodford shales in the 23,000 sq mi (60,000 sq km) geographic area of southern and western Oklahoma underlain by the Woodford Formation. Minimum relative oil-expulsion efficiency appears to have been approximately 18 to 19% of the oil generate . Thus, at least 27 billion bbl of oil have been expelled from the Woodford into adjacent formations in southern and western Oklahoma while 120 billion bbl of oil remain unexpelled in the source rock.

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