Stored formation/play groups ranked by recorded well count, with recorded operators and primary counties. Coverage is limited to the groups included below.
Buckhead Energy analysis of public oil and gas data. Daily refresh scheduled. Stored source refresh: 2026-11-01.
Stored source refresh: 2026-11-01. Formation/play groups require at least 25 recorded wells and a known operator; the directory shows at most 50 groups ranked by well count. Operator counts reflect distinct recorded operator names, not verified current operations. Permit counts use the preceding 24 months at summary refresh. Grouping can represent a formation, play or basin; it is not an inventory of every geological formation. Figures are Buckhead Energy analysis of public oil and gas data; counts under 3 wells are withheld.
Buckhead Energy analysis of public oil and gas data. Scheduled refreshes do not guarantee that new regulator filings are available; the state regulator remains the record of any specific well.
Quick answer: The highest well-count groups listed for Illinois are the Illinois Basin, Wisconsin Arch, Michigan Basin, New Albany and Lake Michigan, led by the Illinois Basin with 199,361 wells on record. Ranked by well count across 5 tracked formations from Buckhead Energy analysis of public oil and gas data. Stored source refresh: 2026-11-01. These are limited stored records; reporting windows are evaluated at source refresh.
The highest well-count groups listed for Illinois are the Illinois Basin, Wisconsin Arch, Michigan Basin, New Albany and Lake Michigan, led by the Illinois Basin with 199,361 wells on record. Ranked by well count across 5 tracked formations from Buckhead Energy analysis of public oil and gas data. Stored source refresh: 2026-11-01. These are limited stored records; reporting windows are evaluated at source refresh.
Top Operators:
The Ohio Oil (10,768), Marathon Oil Company (4,511), The Texas Company (4,094), Pure Oil Company (3,226), Texaco (2,426), Ohio Oil Company (2,180), The Pure Oil Company (1,931), 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), Perry Edward (10), Snelton Brothers (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), Midwestern Gas Transmission Company (7), Kelley Conrad & Kaye (7), Penntex Resources Illinois (7), Forest Oil (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 (—)
Primary counties: Lake, Cook
Source: Buckhead Energy analysis of public oil and gas data, aggregated by primary play / interpreted formation / basin.
Threshold: Groups require at least 25 recorded wells and a known operator. The directory shows up to 50 groups by well count; omitted groups are not evidence of no activity.
Owner context: These formation summaries describe reported activity. They do not establish ownership, payment entitlement or a value for an individual tract.
Refresh cadence: Daily refresh scheduled. Stored source refresh: 2026-11-01.
The highest well-count formation/play groups listed for Illinois are the Illinois Basin, Wisconsin Arch, Michigan Basin, New Albany and Lake Michigan, among others. This directory tracks 5 recorded formation/play groups ranked by well count, per Buckhead Energy analysis of public oil and gas data. Stored source refresh: 2026-11-01. These are limited stored records; reporting windows are evaluated at source refresh.
The Illinois Basin has the most wells among the listed Illinois groups — 199,361 wells, worked by 13,021 recorded operators, per Buckhead Energy analysis of public oil and gas data. This is a well-count ranking, not a reserves or value ranking. Stored source refresh: 2026-11-01. These are limited stored records; reporting windows are evaluated at source refresh.
The operators with the most wells on record 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. Stored source refresh: 2026-11-01. These are limited stored records; reporting windows are evaluated at source refresh.
About 483 drilling permits were filed across the tracked Illinois formations in the 24-month window at source refresh, per Buckhead Energy analysis of public oil and gas data — a rough measure of where new activity is concentrated. Stored source refresh: 2026-11-01. These are limited stored records; reporting windows are evaluated at source refresh.
Your deed and county records determine which formations your mineral rights cover; a tract can own multiple stacked formations. This directory is informational only, not a valuation. Stored source refresh: 2026-11-01. These are limited stored records; reporting windows are evaluated at source refresh.
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Get Your Free Written OfferState: Illinois
Active formations: 5
Total wells: 204,212
Recent permits: 483
Last refresh: 2026-11-01
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