Every active oil and gas formation and play in Illinois — Illinois Basin, Wisconsin Arch, Michigan Basin, New Albany, Lake Michigan, and more — ranked by well count, with the top operators and primary counties for each.
Refreshed monthly from IDNR well records. Data current as of 2026-08-02.
Quick answer: The most-targeted oil and gas formations in Illinois are the Illinois Basin, Wisconsin Arch, Michigan Basin, New Albany and Lake Michigan, led by the Illinois Basin with 199,282 wells on record. Ranked by well count across 5 tracked formations from Illinois Department of Natural Resources (IDNR) well-header records (as of 2026-08-02) and refreshed monthly.
As of 2026-08-02, the most-developed Illinois formation is the Illinois Basin with 199,282 wells on record, across 5 tracked formations, per Illinois Department of Natural Resources (IDNR) well records.
Top Operators:
The Ohio Oil (10,768), Marathon Oil Company (4,511), The Texas Company (4,094), Pure Oil Company (3,187), Texaco (2,426), Ohio Oil Company (2,179), The Pure Oil Company (1,943), The Carter Oil (1,811), Forest Oil (1,671), Magnolia Petroleum Company (1,602)
Primary counties: Crawford, White, Lawrence, Wayne, Peoria
Top Operators:
Il State Geological Survey (421), Natural Gas Pipeline CO Of America (411), Vickery Drilling (404), Northern Illinois Gas Company (314), Natural Gas Storage Company Of Il (176), Wang Engineering (145), Central Il Electric (135), Alco Oil & Gas (112), Bays Carl A Etal (87), Peoples Gas & Companyke Company (81)
Primary counties: Will, Mc Henry, Kane, Winnebago, Du Page
Top Operators:
Il State Geological Survey (193), Illinois State Geological Survey (74), Miller J P Art Well (28), Isgs (26), Keiferassociates (25), Northern Illinois Gas Company (24), Alco Oil & Gas (16), Geiger S B Company (13), Snelton Brothers (10), Perry Edward (10)
Primary counties: Lake, Cook, Mc Henry, Du Page, Will
Top Operators:
Dayton Ward W (31), National Associated Petroleum Company (23), Marathon Oil Company (18), The Ohio Oil (14), Zink Earnest (11), Kelley Conrad & Kaye (7), Forest Oil (7), Midwestern Gas Transmission Company (7), Penntex Resources Illinois (7), Hf Sinclair Corporation (6)
Primary counties: Jersey, Clark, Lawrence, Edgar, Crawford
Top Operators:
Illinois State Geological Survey (36), Il State Geological Survey (11), Hester N C (9), Mattheus Spitzer And Pearce (4), U S Geological Survey (1)
Primary counties: Lake, Cook
Source: Illinois Department of Natural Resources (IDNR) well-header records, aggregated by primary play / interpreted formation / basin.
Threshold: Only formations with at least 50 wells are listed (excludes one-off wildcat plays).
Why it matters: Knowing which formation underlies your tract — and which operators are actively drilling that formation — is the foundation of mineral-rights valuation. Stacked-pay plays carry materially different upside than mature single-bench plays.
Refresh cadence: Monthly. Data current as of 2026-08-02.
Cite this dataset
Permanently archived and citable via a DOI on Zenodo (CERN), under a CC BY 4.0 license. DOI: 10.5281/zenodo.21442884 · View on Zenodo
License & attribution: This data is licensed CC BY 4.0. You are free to share and adapt it, including commercially, provided you credit “Buckhead Energy” and link back to this page or the DOI above.
The most-developed formations and plays in Illinois are the Illinois Basin, Wisconsin Arch, Michigan Basin, New Albany and Lake Michigan, among others. This directory tracks 5 active formations ranked by well count, per Illinois Department of Natural Resources (IDNR) records.
The Illinois Basin has the most wells on record in Illinois — 199,282 wells, worked by 13,020 active operators, per IDNR well-header data. This is a well-count ranking, not a reserves or value ranking.
The most active operators in the Illinois Basin are The Ohio Oil, Marathon Oil Company, The Texas Company, Pure Oil Company, Texaco. Each formation card below lists its top operators by well count.
About 508 drilling permits were filed across the tracked Illinois formations in the last 24 months, per IDNR records — a rough measure of where new activity is concentrated.
Your deed and county records determine which formations your mineral rights cover; a tract can own multiple stacked formations. Buckhead Energy can check the geology under your tract against current well and permit data and put a free, no-obligation written offer in writing — this directory is informational only, not a valuation.
The geology under your tract drives your valuation. Get a free written offer based on your specific formation and county.
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Sell Your Illinois Mineral Rights
State: Illinois
Active formations: 5
Total wells: 204,133
Recent permits: 508
Last refresh: 2026-08-02
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