What was assessed
The U.S. Geological Survey estimated the undiscovered, technically recoverable conventional oil and gas in eight geologic provinces of the Greater Caspian area, using a geology-based method: the North Caspian, North Ustyurt, Middle Caspian, Azov-Kuban, South Caspian, Kura, Dnieper-Donets and Pripyat basins.
Figure 1. The eight assessed provinces. Base map from the U.S. Department of the Interior, National Park Service. USGS.
Geology
The region's petroleum systems reflect the complex tectonic history of the continental margin of northeast Pangaea, which bordered the Paleotethys and Neotethys Oceans. Most of the basins are polyphase: their present shape comes from several tectonic processes. Room for sediment to accumulate was created by subsidence in rifts, back-arc and intra-arc basins, thermal sag basins and foreland basins, alone or in combination.
The USGS defined a total petroleum system (TPS) in each province, named for the age of its main source rocks:
| Source rocks | Where | What they are |
|---|---|---|
| Paleozoic | Dnieper-Donets, Pripyat, North Caspian and North Ustyurt | organic-rich marls in carbonate basins; Devonian marine shales laid down during and after rifting; Carboniferous marine shales, marls and coals; carbonaceous shales |
| Mesozoic | North Ustyurt, Middle Caspian, Azov-Kuban, South Caspian, Kura | Jurassic and Cretaceous organic-rich carbonate marls; Jurassic lake shale, coal beds and carbonaceous shale |
| Cenozoic | same basins | mainly the organic-rich marine shales of the Oligocene–Miocene Maykop Formation, and possibly diatomites |
Within these systems it defined 15 assessment units (AUs) and assessed each one.
Results
The mean totals, fully risked, are:
| Mean | Range (F95–F5) | |
|---|---|---|
| Oil | 34,335 million barrels (34.3 billion) | 13,519–67,172 million barrels |
| Gas | 319,574 billion cubic feet (320 trillion) | 122,871–626,967 billion cubic feet |
| Natural gas liquids | 7,421 million barrels (7.4 billion) | 2,858–14,628 million barrels |
F95 is a 95 percent chance of at least that amount; F5 a 5 percent chance.
Mean undiscovered resources by assessment unit — oil and gas in oil fields, and gas in gas fields:
| Assessment unit | Oil (million barrels) | Gas in oil fields (billion cu ft) | Gas in gas fields (billion cu ft) |
|---|---|---|---|
| North Caspian North and West Margin Presalt | 499 | 1,398 | 12,261 |
| North Caspian South and East Margin Presalt | 7,443 | 11,163 | 29,960 |
| North Caspian Postsalt | 1,288 | 1,030 | 8,618 |
| North Ustyurt Paleozoic | 56 | 56 | 13,816 |
| North Ustyurt Mesozoic–Cenozoic | 596 | 238 | 7,867 |
| Middle Caspian Central Basin–South Mangyshlak | 2,178 | 5,444 | 26,655 |
| Middle Caspian North Caucasus Platform | 2,576 | 3,349 | 1,881 |
| Middle Caspian Terek Foredeep–North Apsheron | 504 | 908 | 2,375 |
| Azov-Kuban Foredeep | 318 | 541 | 800 |
| Azov-Kuban Foreland | 47 | 52 | 2,877 |
| South Caspian Marginal Fold Belt | 5,384 | 14,536 | 29,225 |
| South Caspian Central Depression | 12,378 | 33,421 | 96,099 |
| Kura Basin | 752 | 376 | 2,307 |
| Dnieper-Donets Paleozoic | 199 | 837 | 11,391 |
| Pripyat Paleozoic | 117 | 93 | — |
The South Caspian Central Depression holds the largest share of both oil and gas. The Pripyat unit was assessed for oil only.
Key input data — the expected number and size of undiscovered fields in each unit — are in the fact sheet and in the USGS data release (Schenk, 2025). Results are also on the USGS Energy Resources Program website.
Sources
Based on Greater Caspian Assessment Team (Christopher J. Schenk and others), "Assessment of undiscovered conventional oil and gas resources of the Greater Caspian area, 2022," U.S. Geological Survey Fact Sheet 2024–3047; a work of the United States government in the public domain. It cites Otto (1997), Brunet and others (2003), Golonka (2007), Boote and others (2018), Ulmishek (2001), Okere and Toothill (2012), Smith-Rouch (2006) and Sachsenhofer and others (2018, 2021) for the geology.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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