World Petroleum Resources Project Fact Sheet

Introduction

 The U.S. Geological Survey (USGS) estimated technically 

recoverable, conventional, undiscovered oil and gas resources 

of the Caspian Sea area as part of a program to estimate these 

resources for priority basins around the world. Four petroliferous geologic provinces cover the Caspian Sea area, (1) the 

North Caspian Basin, (2) Middle Caspian Basin, (3) North 

Ustyurt Basin, and (4) South Caspian Basin (fig. 1). The provinces encompass approximately 1,315,000 square kilometers 

and were based on interpretations by Delia and others (2008) 

and Natal’in and Şengör (2005). This assessment was based on 

published geologic information and on commercial data from 

oil and gas wells and fields, and field production records. The 

USGS approach is to define total petroleum systems and assessment units, and assess the potential for undiscovered oil and gas 

resources. 

Total Petroleum Systems and Assessment Units

 One total petroleum system (TPS), Paleozoic Composite, 

was defined for the North Caspian Basin Province to include 

source rocks ranging in age from Late Devonian through Early 

Permian (table 1, Ulmishek, 2001b). Five assessment units 

(AU) were defined geologically within this TPS. Four of the 

AUs lie below Lower Permian (Kungarian) evaporites (fig. 2A) 

— North and West Margins Subsalt AU, East and Southeast 

Margins Subsalt AU, South Margin Subsalt AU, and Central 

Basin Subsalt AU (table 1). Most reservoirs and seals in these 

AUs are associated with carbonate shelves and reefs, although 

some shelf and basin-slope clastic reservoirs of poor quality 

exist. Because of the extreme depths, a greater uncertainty was 

assumed that the Central Basin Subsalt AU contains technically 

recoverable oil or gas exceeding the minimum accumulation 

size set for the assessment (0.5 million barrels of oil equivalent) 

and therefore it was assigned a probability of 0.63 (table 1). 

Carbonate reefs and features associated with carbonate shelves 

are important traps for the subsalt AUs. Structural traps and 

likely stratigraphic traps are known in the East and Southeast 

Margins Subsalt AU. The Suprasalt AU lies above the evaporites (fig. 2A). Reservoirs and seals in this AU include clastic 

rocks ranging in age from Late Permian through Cretaceous and 

traps are associated with salt tectonics.

Assessment of Undiscovered Oil and Gas Resources of the 

North Caspian Basin, Middle Caspian Basin, North Ustyurt 

Basin, and South Caspian Basin Provinces, Caspian Sea 

Area, 2010

The U.S. Geological Survey estimated mean volumes of technically recoverable, conventional, undiscovered petroleum resources at 19.6 billion 

barrels of crude oil, 243 trillion cubic feet of natural gas, and 9.3 billion barrels of natural gas liquids for the Caspian Sea area, using a geologybased assessment methodology.

Russia

Iran

Kazakhstan

Iraq

Turkey Turkmenistan

Uzbekistan

Azerbaijan

Georgia

Syria

Armenia

40°E 42°E 44°E 46°E 48°E 50°E 52°E 54°E 56°E 58°E 60°E 64°N

62°N

60°N

58°N

56°N

54°N

52°N

50°N

48°N

46°N

44°N

42°N

40°N

38°N

36°N

34°N

Caspian 

 Sea

Black 

 Sea

Aral 

 Sea

AFRICA

RUSSIA

Arabian Sea

Barents Sea

EXPLANATION

North Caspian

Basin Province

North Ustyurt

Basin Province

Middle Caspian

Basin Province

South Caspian

Basin Province

Assessment Unit (AU)

Basin Center Subsalt AU

South Margin Subsalt AU

Mesozoic-Cenozoic

 Reservoirs AU

Upper Paleozoic

Carbonates AU

Mesozoic-Sandstone 

 Reservoirs AU

 East and 

 Southeast 

 Margins 

Subsalt AU

North and West Margins Subsalt AU

Stavropol-Prikumsk

AU

South

Mangyshlak

AU Foreland Slope AU 

Foldbelt-Foothills AU

Turkmen 

Block AU

Lower 

 Kura 

Depression and 

Adjacent Shelf

AU

0 250 500 MILES

0 250 500 KILOMETERS

Suprasalt AU

Apsheron-Pribalkhan Zone AU

A

B

C

A'

B'

C'

Cross Section

Figure 1. Location of 15 assessment units (AU) in the Caspian Sea 

area and approximate locations of cross sections shown in figure 2. 

(Map not definitive for political boundaries.)

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2010–3094

November 2010 Printed on recycled paper Printed on recycled paper
 Three TPSs were identified in the North Ustyurt Basin 

Province — Buzachi Arch and Surrounding Areas Composite TPS, Mesozoic-Cenozoic Composite TPS, and Paleozoic 

Composite TPS (table 1, Ulmishek, 2001c). The Buzachi Arch 

and Surrounding Areas Composite TPS was defined to include 

source rocks within the Buzachi Arch and possible contributions 

of oil and gas from the neighboring North and Middle Caspian Basins. One AU was defined for each TPS — Mesozoic 

Sandstone Reservoirs AU, Mesozoic-Cenozoic Reservoirs AU, 

and Upper Paleozoic Carbonates AU, respectively. Reservoirs 

and seals are indicated in the AU names. Most known traps are 

structural, although some pinchout traps are inferred.

 The Terek-Caspian, South Mangyshlak, and StavropolPrikumsk TPSs were identified in the Middle Caspian Basin 

Province (table 1, Ulmishek, 2001a). Source rocks in the TerekCaspian TPS include Oligocene to Lower Miocene Maykop 

Formation, Eocene Kuma Formation, and possibly some Middle 

to Upper Jurassic subsalt mudstones. The South Mangyshlak 

TPS includes Triassic and possibly Jurassic source rocks. Lower 

Triassic, Middle Jurassic, and the Oligocene to lower Miocene 

15

10

5

0

Kilometers (Datum Mean Sea Level) Kilometers (Datum Mean Sea Level)

20

EAST AND SOUTHEAST

MARGINS SUBSALT AU

0 100 200 KILOMETERS

0 50 100 MILES

W E

SUPRASALT AU

CENTRAL BASIN

SUBSALT AU

EXPLANATION

1

2

3

4

5

6

7 Fault 8 AU Boundary

KILOMETERS

MILES

 1

 2

0

 1

 2

 3

 4

 5

 6

 7

 8

 9

 10

S N

FORELAND SLOPE

AND FOREDEEP AU STAVROPOL-PRIKUMSK AU

Basement

FOLDBELT

AND

FOOTHILLS

AU

EXPLANATION

1

2

3

4

Fault

AU Boundary

Kilometers (Datum Mean Sea Level) 15

10

5

0

20

25 100 200 KILOMETERS

0 100 MILES

0

50

EXPLANATION

1

2

3

4

5

6 Fault

7

8

9

10

AU Boundary

W E

TURKMEN BLOCK AU

LOWER KURA

DEPRESSION AND

ADJACENT SHELF AU

(offshore continuation)

APSHERONPRIBALKHAN

ZONE AU

LOWER KURA

DEPRESSION AND

ADJACENT SHELF AU

0

0 10 20 30 40 50

10 20 30

A.

B.

C.

A A'

B B'

C C'

Figure 2. Schematic geologic cross sections of the Caspian Sea basins illustrating the geologic delineations of several assessment units (AU) in this 

study. Locations of cross sections shown in figure 1. A. North Caspian Basin Province, modified from Volozh and others (2003). Rock units: 1, Cenozoic; 

2, Mesozoic; 3, Upper Permian; 4, Kungarian salt; 5, Carboniferous to Permian; 6, Devonian to Carboniferous; 7, Lower Paleozoic; 8, Proterozoic. 

B. Middle Caspian Basin Province, modified from Ulmishek (2001a). Rock units: 1, Cenozoic; 2, Cretaceous; 3, Jurassic; 4, Upper Permian to Triassic. 

C. South Caspian Basin Province, modified from Abrams and Narimanov (1997). Rock units: 1, Quaternary; 2, middle to upper Pliocene; 3, lower Pliocene; 4, Miocene; 5, Oligocene to Miocene (Maykop Formation); 6, Paleocene to Eocene; 7, Mesozoic; 8, basement, continental crust; 9, basement, 

oceanic crust; 10, water of the Caspian Sea.
Total undiscovered resources Total Petroleum Systems

(TPS)

and Assessment Units (AU)

Field

type

Oil (MMB) Gas (BCF) NGL (MMB)

F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean

Mean (expected)

largest

field size

(MMB or BCF)

Gas

North and West Margins Oil

Subsalt AU

Gas

Oil East and Southeast Margins

Subsalt AU

Gas

Oil

South Margin Subsalt AU

North Caspian Basin Province, Paleozoic Composite TPS

16 48 127 56

88 331 1,031 414

37

155

250

2,646

Central Basin Subsalt AU

(AU probability = 0.63)

Suprasalt AU

196

663 2,173 6,246 1,544

3,975

Total Undiscovered Resources,

North Caspian Basin 1,278 3,940 10,565 4,671 7,511

Gas

Oil 0 0 0 0 0

0

Gas

Oil 511 1,388 3,161 1,555 1,291

63

17

160

199

633

993

5,954

3,581

309

48

Gas

Oil

Foldbelt-Foothills AU

Gas

Foreland Slope and Oil

Foredeep AU

Middle Caspian Basin Province, Terek-Caspian TPS

66 129 238 138

66 219 618 264

147

144

300

153

28

90

154

369

Gas

Oil

South Mangyshlak AU

145 374 855 422 324

315

Total Undiscovered Resources,

Middle Caspian Basin 569 1,625 4,200 1,908 2,408

116

293

Gas

Oil

Stavropol-Prikumsk AU

292 903 2,489 1,084 629

396

399

803

Middle Caspian Basin Province, South Mangyshlak TPS

Middle Caspian Basin Province, Stavropol-Prikumsk TPS

Gas

Mesozoic Sandstone Oil

Reservoirs AU

North Ustyurt Basin Province, Buzachi Arch and Surrounding Areas Composite TPS

97 250 592 285 35

76

68

261

Gas

Mesozoic-Cenozoic Oil

Reservoirs AU

21 51 115 57 7

370

Total Undiscovered Resources,

North Ustyurt Basin 118 301 707 342 1,339

95

373

Gas

Upper Paleozoic Oil

Carbonates AU

0 0 0 0 0

851

21

425

North Ustyurt Basin Province, Mesozoic-Cenozoic Composite TPS

North Ustyurt Basin Province, Paleozoic Composite TPS

Gas

Apsheron-Pribalkhan Oil

Zone AU

Gas

Lower Kura Depression and Oil

Adjacent Shelf AU

Gas

Oil

Turkmen Block AU

South Caspian Basin Province, Cenozoic Composite TPS

349 897 1,997 1,001

634 2,938 10,744 3,947

981

1,743

319

7,723

3,859

1,375 6,025 19,802 13,929

17,499

Total Undiscovered Resources,

South Caspian Basin 2,358 9,860 32,543 38,330

111

593

736

879

5,051

13,070

25,874

0

1,515

3,750

169

309

512

616

599

879

824

7,098

1,994

1,365

92

300

19

953

3,888

0

2,524

2,608

8,377

1,382

17,659

61,698

64,405

156,129

296

1,907

1,877

3,606

14,550

37,194

83,623

0

14,574

9,200

419

620

1,586

1,187

2,133

2,223

1,972

20,362

5,930

4,711

228

1,270

45

2,282

10,587

0

6,762

6,312

33,632

6,226

64,260

205,402

178,526

494,358

2

12

24

28

104

424

4,054

0

49

3,404

7

6

11

16

16

57

35

283

91

51

2

6

1

20

48

0

19

32

104

51

654

936

1,354

3,131

6

40

62

118

311

1,227

11,153

0

475

8,897

17

13

33

32

57

152

86

850

294

183

6

29

1

52

140

0

52

80

427

235

2,469

3,140

3,898

12,671 10,249

1

3

8

6

32

129

1,294

0

0

1,112

3

3

3

8

4

21

13

94

28

14

1

2

<1

8

17

0

6

12

21

12

141

211

363

760

259

1,731

1,149

10,354

3,101

24,901

Total Undiscovered Petroleum

Resources, Caspian Sea Area

3

16

28

41

129

518

4,864

0

117

4,004

8

7

13

17

21

68

40

352

117

69

3

10

1

24

61

0

23

38

149

78

889

1,207

1,641

4,002

19,592 9,279

131

755

859

6,160

15,858

1,242

33,099

0

3,592

4,307

195

336

642

662

795

1,023

940

8,655

2,468

1,789

107

438

22

1,091

4,651

0

2,993

2,997

11,833

2,065

79,223

77,085

23,632

196,835

243,240

Table 1. Caspian Sea area assessment results (technically recoverable, conventional undiscovered resources). 

[MMB, million barrels; BCF, billion cubic feet. Results shown are fully risked estimates. For gas fields, all liquids are included under the natural gas liquids (NGL) category. F95 denotes a 95-percent chance of at least the amount tabulated. Other fractiles are defined similarly. Fractiles 

are additive under the assumption of perfect positive correlation. TPS, total petroleum system; AU, assessment unit. Gray shading indicates not 

applicable]
Maykop Formation are source rocks in the Stavropol-Prikumsk 

TPS. Two AUs were defined for the Terek-Caspian TPS — 

Foldbelt-Foothills AU and Foreland Slope and Foredeep AU 

(fig. 2B). Reservoirs and seals in these AUs are mainly Upper 

Cretaceous to Eocene carbonate rocks and Lower to Upper 

Cretaceous and Miocene clastic rocks. One AU was defined 

for each of the other TPSs, having the same names as the TPS 

— South Mangyshlak AU and Stavropol-Prikumsk AU (fig. 2B, 

table 1). In the South Mangyshlak AU, reservoirs and seals 

exist in Lower to Middle Jurassic and Cretaceous clastic rocks, 

Triassic carbonates, and in fractured and weathered basement 

granite. Triassic carbonate rocks; Jurassic, Cretaceous, and Oligocene clastic rocks; and fractured Maykop mudstone provide 

reservoirs and seals in the Stavropol-Prikumsk AU. Known 

traps in all of the AUs are mostly structural, with some pinchout 

and stratigraphic traps.

 The Cenozoic Composite TPS was defined for the South 

Caspian Basin Province (table 1) to include Oligocene to lower 

Miocene Maykop Formation and overlying Diatom Formation 

marine source rocks, and possibly also Eocene marine source 

rocks. The Apsheron-Pribalkhan Zone, Lower Kura Depression 

and Adjacent Shelf, and Turkmen Block AUs were defined in 

the TPS (fig. 2C). Reservoir and seal rocks are predominantly 

Pliocene to Pleistocene clastic rocks. Known traps include both 

structural and stratigraphic.

Assessment Results

 Estimates of volumes of technically recoverable, conventional, undiscovered oil and gas resources are shown in table 1. 

No attempt was made to estimate economically recoverable 

resources because it is beyond the scope of this study. The combined mean undiscovered petroleum resources in the Caspian 

Sea area are 19.6 billion barrels of recoverable crude oil, 243 

trillion cubic feet of recoverable natural gas, and 9.3 billion barrels of recoverable natural gas liquids.

 In the North Caspian Basin Province, the mean volumes 

and probability ranges (F95 to F05) of undiscovered petroleum 

are approximately 4,671 million barrels (MMB) of crude oil, 

with a range of 1,278 to 10,565 MMB; 33,099 BCF of natural 

gas (both associated and dissolved, and nonassociated), with 

a range of 7,511 to 83,623 billion cubic feet (BCF); and 4,864 

MMB of natural gas liquids, with a range of 1,294 to 

11,153 MMB.

 In the North Ustyurt Basin Province, the mean volumes 

and probability ranges (F95 to F05) of undiscovered oil are 

approximately 342 MMB of crude oil, with a range of 118 

to 707 MMB; 4,651 BCF of natural gas (both associated and 

dissolved, and nonassociated), with a range of 1,339 to 10,587 

BCF; and 61 MMB of natural gas liquids, with a range of 17 to 

140 MMB.

 In the Middle Caspian Basin Province, the mean volumes 

and probability ranges (F95 to F05) of undiscovered oil are 

approximately 1,908 MMB of crude oil, with a range of 569 

to 4,200 MMB; 8,655 BCF of natural gas (both associated and 

dissolved, and nonassociated), with a range of 2,408 to 20,362 

BCF; and 352 MMB of natural gas liquids, with a range of 94 to 

850 MMB.

 In the South Caspian Basin Province, the mean volumes 

and probability ranges (F95 to F05) of undiscovered oil are 

approximately 12,671 MMB of crude oil, with a range of 2,358 

to 32,543 MMB; 196,835 BCF of natural gas (both associated 

and dissolved, and nonassociated), with a range of 38,330 to 

494,358 BCF; and 4,002 MMB of natural gas liquids, with a 

range of 760 to 10,249 MMB.

References Cited

Abrams, M.A., and Narimanov, A.A., 1997, Geochemical 

evaluation of hydrocarbons and their potential sources in the 

western South Caspian depression, Republic of Azerbaijan: 

Marine and Petroleum Geology, v. 14, no. 4, p. 451–468.

Delia, S.V., Kerusov, I.N., Kosova, S.S., and Shilkin, S., 2008, 

Principal stages and specific features of geotectonics in the 

northern part of the Middle Caspian [abs]: European Association of Geoscientists and Engineers Conference Petroleum 

Geology and Hydrocarbon Potential of Caspian and Black 

Sea Regions, 6–8 October 2008, Baku, Azerbaijan, A17.

Natal’in, B.A., and Şengör, A.M.C., 2005, Late Paleozoic to 

Triassic evolution of the Turan and Scythian platforms: The 

pre-history of the Palaeo-Tethyan closure: Tectonophysics, 

v. 404, p. 175–202.

Ulmishek, G.F., 2001a, Petroleum geology and resources of the 

Middle Caspian Basin, Former Soviet Union: U.S. Geological Survey Bulletin 2201–A, 38 p.

Ulmishek, G.F., 2001b, Petroleum geology and resources of the 

North Caspian Basin, Kazakhstan and Russia: U.S. Geological Survey Bulletin 2201–B, 25 p.

Ulmishek, G.F., 2001c, Petroleum geology and resources of 

the North Ustyurt Basin, Kazakhstan and Uzbekistan: 

U.S. Geological Survey Bulletin 2201–D, 14 p.

Volozh, Yu.A., Antipov, M.P., Brunet, M.-F., Garagash, I.A., 

Lobkovshii, L.I., and Cadet, J.-P., 2003, Pre-Mesozoic geodynamics of the Precaspian Basin (Kazakhstan): Sedimentary 

Geology, v. 156, p. 35–58.

For Further Information

 Publications detailing the geology and the methodology 

for the Caspian Sea area and assessment results are available at 

the USGS Energy Program Web site, http://energy.cr.usgs.gov/

oilgas/.

Caspian Sea Area Assessment Team

 T.R. Klett (tklett@usgs.gov), Christopher J. Schenk, Ronald R. Charpentier, Donald L. Gautier, Michael E. Brownfield, 

Janet K. Pitman, Troy A. Cook, and Marilyn E. Tennyson.

Acknowledgments

 Geographic Information Systems support by Christopher P. 

Anderson, ATA Services. Graphic support by Wayne Husband, 

ATA Services.