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.
[Illustration: 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.]
[Illustration: 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