Illinois has been producing oil longer than almost any other state. The first commercial oil well in Illinois was completed in 1853 — six years before Edwin Drake's famous Pennsylvania well. Over the next 170 years, Illinois operators drilled more than 100,000 oil wells. The state's long production history has created an incredibly rich dataset of geological information.
The Illinois Basin
The Illinois Basin is a structural depression that sits under most of Illinois and extends into western Kentucky and southwestern Indiana. It is one of the oldest petroleum-producing basins in the country. Oil is found in multiple formations, including the McClosky, Aux Vases, and Cypress sandstone formations. These are conventional reservoirs — the oil sits in porous rock and flows to the well without needing hydraulic fracturing. However, most of these fields have been producing for decades and are in decline.
How Much Does Illinois Produce?
Illinois currently produces around 20,000 to 25,000 barrels of oil per day. This is much less than its historical peak but still makes it a notable producer in the Midwest. There is very little natural gas production — Illinois is primarily an oil state. The southern part of the state, particularly around the Wayne, Hamilton, and White counties, has the highest concentration of active wells.
Who Regulates Illinois Wells?
The Illinois Department of Natural Resources (DNR) — Office of Oil and Gas oversees drilling permits, production reporting, and well plugging. Illinois has a large number of orphan wells — abandoned wells with no responsible operator — and the DNR has an active program to locate and plug them. Public well data is searchable at dnr.illinois.gov/oilandgas.html.
Why Illinois Well Data Is Valuable
With over 170 years of drilling records, Illinois has some of the most comprehensive historical well data of any state. Geologists studying shallow conventional plays in the Midcontinent region can use Illinois data to understand formation characteristics, typical production rates, and how fields decline over time. This kind of data is invaluable for prospect evaluation even in other states with similar geology.