Every active oil and gas formation and play in California — Monterey-Temblor, San Joaquin Basin, Monterey, Sacramento Basin, Coastal Basins, Los Angeles Basin, and more — ranked by well count, with the top operators and primary counties for each.
Refreshed monthly from CalGEM well records. Data current as of 2026-08-16.
Quick answer: The most-targeted oil and gas formations in California are the Monterey-Temblor, San Joaquin Basin, Monterey, Sacramento Basin and Coastal Basins, led by the Monterey-Temblor with 96,601 wells on record. Ranked by well count across 16 tracked formations from California Geologic Energy Management Division (CalGEM) well-header records (as of 2026-08-16) and refreshed monthly.
As of 2026-08-16, the most-developed California formation is the Monterey-Temblor with 96,601 wells on record, across 16 tracked formations, per California Geologic Energy Management Division (CalGEM) well records.
Top Operators:
Aera Energy (44,660), Chevron (16,193), California Resources Elk Hills LLC (7,377), Berry Petroleum Company (7,207), Sentinel Peak Resources Ca (5,640), California Resources Production (5,275), Crimson Resource Management (1,760), Holmes Western Oil (1,012), Shell Oil Company (604), Mobil Oil (420)
Primary counties: Kern, Kings, Fresno, Tulare
Top Operators:
Chevron (34,514), Aera Energy (8,885), California Resources Production (5,598), E & B Natural Resources Management (3,032), Sentinel Peak Resources Ca (2,823), Macpherson Oil Company (1,236), Berry Petroleum Company (1,175), Shell Oil Company (537), Bellaire Oil Company (535), Hunter Edison Oil Development LTD (525)
Primary counties: Kern, Fresno, Tulare, San Benito, Madera
Top Operators:
Chevron (4,975), Tidelands Oil Production Company (3,825), Aera Energy (2,634), California Resources Production (2,209), Union Oil Company Of California (1,931), Calnrg Operating LLC (1,919), Thums Long Beach Company (1,893), Sentinel Peak Resources Ca (1,657), Exxon Mobil (1,210), Union Pacific Resources Company (898)
Primary counties: Los Angeles, Orange, Ventura, Santa Barbara, Los Angeles Offshore
Top Operators:
California Resources Production (1,861), Chevron (755), Atlantic Oil Company (316), Amerada Hess (260), Capitol Oil (217), Shell Oil Company (174), Phillips Petroleum Company (166), Exxon Mobil (164), Pacific Gas & Electric Company (162), Rosetta Resources Operating (157)
Primary counties: Solano, Yolo, Colusa, Glenn, San Joaquin
Top Operators:
Chevron (1,810), Aera Energy (1,532), Sentinel Peak Resources Ca (526), Shell Oil Company (193), Phillips Petroleum Company (70), E & B Natural Resources Management (65), Calnrg Operating LLC (59), Exxon Mobil (57), Grace Petroleum (53), Arco Oil & Gas Company (51)
Primary counties: Monterey, San Luis Obispo, Kern, San Benito, Santa Barbara
Top Operators:
Shadow Wolf Energy LLC (535), Chevron (356), Sentinel Peak Resources Ca (283), Southern Community (257), West Energy Operating LLC (119), Warren E & P (116), Caltico Oil (94), Thums Long Beach Company (88), The Termo Company (67), Crimson Resource Management (63)
Primary counties: Los Angeles, Orange, Los Angeles Offshore, San Bernardino, Ventura
Top Operators:
Carbon California Operating Company LLC (606), Chevron (245), Calnrg Operating LLC (229), Shell Oil Company (102), Union Oil Company Of California (74), The Termo Company (53), Argo Petroleum (49), Arco Oil & Gas Company (48), American Oil (46), Adolfo Camarillo (46)
Primary counties: Ventura, Los Angeles, Ventura Offshore, Santa Barbara
Top Operators:
E & B Natural Resources Management (376), Sunset Oil Company (187), Arco Oil & Gas Company (108), Chevron (102), Seaside Oil Company (86), Saba Petroleum (69), Oryx Energy Company (55), Southern Community (34), Atlantic Richfield Company (34), Phillips Petroleum Company (31)
Primary counties: Santa Barbara, Santa Barbara Offshore, San Luis Obispo, Santa Rosa Island, Santa Cruz Area
Top Operators:
Tidelands Oil Production Company (285), California Resources Production (230), Beta Operating Company (138), Thums Long Beach Company (133), Dcor (37), Chevron (16), City Of Newport Beach (16), Union Pacific Resources Company (10), Exxon Mobil (9), Armstrong Petroleum (7)
Primary counties: Los Angeles, Orange, Santa Catalina Area, Los Angeles Offshore, Orange Offshore
Top Operators:
Cardox CORP (125), Prado Petroleum (14), Chevron (8), The Hampton Oil (6), California Time Petroleum (5), Lynnhart Company INC (4), J B Nelson (4), Pacific-Imperial Dri-Ice INC (4), A L Hunter Oper (3), 104 Oil & Drilling Company (3)
Primary counties: Imperial, Riverside, San Bernardino
Top Operators:
Chevron (35), Patriot Resources (21), Sargent Oil Company (20), H W Covert (14), E & B Natural Resources Management (12), Petaluma Oil & Gas Development Company (11), Hershey Oil (9), Mobil Oil (8), E C Brown Operator (7), Shell Oil Company (7)
Primary counties: Santa Clara, Alameda, Sonoma, Napa, Mendocino
Top Operators:
Neaves Petro Developments (40), Chevron (26), Union Oil Company Of California (22), Costa Loma (22), The Eric And Susan Dunn Living Trust Dated July 27 2006 (11), Botto & Miller Trustees (7), Peninsula Open Space Trust (6), Exxon Mobil (6), Shell Oil Company (5), Ziaverde (5)
Primary counties: San Mateo, Santa Cruz, Marin, Monterey
Top Operators:
Dcor (39), Union Oil Company Of California (16), Venoco (16), Fred E Cole (15), Calnrg Operating LLC (12), Arco Oil & Gas Company (11), Exxon Mobil (10), Transoceanic Oil (10), Atlantic Richfield Company (7), Sable Offshore CORP (6)
Primary counties: Santa Barbara, Santa Cruz Area, Santa Barbara Offshore, Ventura, Ventura Offshore
Top Operators:
Optima Conservation Resources Exploration (16), Stone Cabin Resources (13), Padre Oil Company (11), Polaris Production (9), Chevron (6), Casex Company (6), L H Scott (4), Mobil Oil (4), Charles C Carrillo & Chris B Pedersen (4), The Major Oil (4)
Primary counties: San Bernardino, Riverside
Top Operators:
California Resources Production (44), Pacific Gas & Electric Company (23), Chevron (16), Harvest Petroleum (13), Zephyr Oil Company (11), Arco Western Energy (8), Jas E Babcock (6), Natural Gas CORP Of Calif (4), Energy Development (3), Argo Petroleum (3)
Primary counties: Humboldt, Del Norte
Top Operators:
Community Oil Well (4), V O D Oil (3), Borderland Exploration (3), Charles F Holmes (2), Grober And Assoc (2), The Macgregor (2), San Diego Sorrento Oil Company (1), Linda Vista Oil Company (1), Cardiff Oil (1), La Jolla Petro Company (1)
Primary counties: San Diego
Source: California Geologic Energy Management Division (CalGEM) 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 2026-08-16.
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 California are the Monterey-Temblor, San Joaquin Basin, Monterey, Sacramento Basin and Coastal Basins, among others. This directory tracks 16 active formations ranked by well count, per California Geologic Energy Management Division (CalGEM) records.
The Monterey-Temblor has the most wells on record in California — 96,601 wells, worked by 946 active operators, per CalGEM well-header data. This is a well-count ranking, not a reserves or value ranking.
The most active operators in the Monterey-Temblor are Aera Energy, Chevron, California Resources Elk Hills LLC, Berry Petroleum Company, Sentinel Peak Resources Ca. Each formation card below lists its top operators by well count.
About 9,986 drilling permits were filed across the tracked California formations in the last 24 months, per CalGEM 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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State: California
Active formations: 16
Total wells: 246,524
Recent permits: 9,986
Last refresh: 2026-08-16
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