Oil Shale
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.