Illinois has a large oil-producing industry that obtains oil from wells.
The state also contains beds of shale that yield oil when the shale is
heated.
In order to estimate the present and future importance of the oil shale
resources, the Survey collected and tested more than 100 shale samples
from 41 Illinois counties. A few samples contained more than 25 gallons
of oil per ton of shale, but most contained less than 15 gallons per
ton. A study of the crude oil distilled from selected shale samples
showed it to be somewhat different from the oil that comes from wells.
It could, nevertheless, be made to yield gasoline, fuel oil, and other
products if suitably processed.
The shale strata generally the richest in oil are found above coal
seams, are black, and are sometimes called slate by coal miners. They
are rarely more than 3 feet thick, but they extend over large areas.