The new fields of southeastern Illinois are within 30 miles of the old fields of Crawford and Lawrence counties. Discoveries have been made in Wayne, Clay, and Richland counties in a belt about 20 miles long.

Studies of information furnished by old shallow tests, followed by torsion-balance and reflection-seismograph surveys, led to the drilling of the discovery wells. The anticlinal ridge on which the new fields are developing is an extension southwest of the Oakland anticline of Edgar and Clark counties. Oil is produced from the McClosky, an oolitic "pay" in the St. Genevieve limestone of Lower Mississippian age. The McClosky is the principal producing horizon in the south end of the old fields of Lawrence County.

Two sands above the St. Genevieve in the lower Chester have shown oil, but since all wells so far have been drilled to the McClosky, these sands have not been tested to any extent.