Petroleum
In recent years production of petroleum has averaged about 78 million barrels each year, making Illinois the eighth largest petroleum producing state. The major oil area is the deep part of the Illinois Basin in the southcentral and southeastern parts of the state, but significant discoveries have been made recently in central and western Illinois. There are about 490 oil fields in Illinois, ranging from a few to several thousand acres in size.
Oil has been discovered in rocks of the Pennsylvanian, Mississippian, Devonian, Silurian, and Ordovician Systems, but the Mississippian are the most productive and account for about 76 percent of our total oil production.
Figure 8—Oil pools in Illinois as of January 1, 1961. The pools are concentrated mainly in the Illinois Basin and along the LaSalle Anticlinal Belt.
Figure 9—Active coal mines are scattered around the margin of the basin where the coals are at relatively shallow depths.
KEY SHIPPING MINES Underground Strip Slope LOCAL MINES OVER 25,000 TONS Underground Strip