The St. Jacob field, on the west flank of the Southern Illinois Coal basin 23 miles east by northeast of St. Louis, Missouri, was discovered in May, 1942. Accumulated production on October 1, 1947, was 1,847,966 barrels of oil and the average production during September was 567 barrels of oil daily from 48 wells. The field is on 20-acre spacing and the productive area covers approximately 1,000 acres. The oil occurs in porous zones in the Trenton (Kimmswick or Galena) limestone formation, and the wells are completed at an average depth of 2,370 feet.

The St. Jacob field comprises two distinct pools separated by a pronounced saddle and characterized by differences in oil-water contact levels, reservoir energy, volume of water, and corrosive nature of the water.

The structure of the north pool is a dome-like anticline, slightly elongate east-northeast and west-southwest, and the structure of the south pool is an asymmetrical anticline with north and south elongation. Reverse or west dip of 186 feet has been established on the south anticline which is an indication of the amount of closure.

The strata below the Pleistocene till or glacial drift are represented by the following sequence of beds in descending order: the Pennsylvanian series, the Upper Mississippian or Chester series, the Lower Mississippian including the St. Louis limestone, Salem limestone and Osage group, the New Albany shale, the Devonian limestone, the Silurian limestone and dolomite, the Maquoketa shale, and the Trenton (Kimmswick or Galena) limestone.

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