The Omaha pool was discovered in November, 1940, by the Carter Oil Company's York No. 1, SE. 1/4, SE. 1/4, SW. 1/4 of Sec. 33, T. 7S., R. 8 E., Gallatin County, Illinois. The producing area is now defined and extends over 450 acres located generally southwest of the discovery well. Production is from the Palestine and Tar Springs formations of the Chester (Upper Mississippian) series.

The pool is on the crest of a large dome and is exceptional in that igneous rock is found in intrusive contact with the producing sands. Sills and dikes ranging from less than one foot to 50 feet in thickness, composed of mica-peridotite, occur at many levels in the Pennsylvanian and Chester series.

Contact effects indicate that some oil was in the sands before intrusion of the igneous material, suggesting a certain amount of prior uplift. The pronounced doming of the structure and the intrusion of dikes and sills may have accompanied intrusion of a hypothetical subjacent laccolithic or stock-like igneous body, probably in post-Pennsylvanian-pre-Cretaceous time. Minor folding occurred earlier at the close of the Mississippian period.