The production of oil in Indiana

The chief oil production of Indiana during the earlier years of development came from the Trenton limestone of the Ordovician in the east central part of the state, the highest annual state yield, 13,000,000 barrels in 1904, marking the climax of this production. In later years new fields in the southwestern part of the state have been discovered, the oil coming chiefly from the Chester series, Upper Mississippian, and the Pottsville and Allegheny series of the Pennsylvanian. At present approximately two-thirds of the oil production of Indiana comes from this district. Subsurface study shows that the oil- and gas-producing structures are generally asymmetrical anticlines with small superimposed domes. There are untested areas and horizons that offer possibilities of new production.