Introduction

The authors of this report summarize 

a geology-based assessment of undiscovered conventional oil and gas resources of 

priority geologic provinces of the world, 

completed between 2009 and 2011 as part 

of the U.S. Geological Survey (USGS) 

World Petroleum Resources Project 

(fig. 1). One hundred seventy-one

geologic provinces were assessed in 

this study (exclusive of provinces of 

the United States), which represent a 

complete reassessment of the world since 

the last report was published in 2000 

(U.S. Geological Survey World Energy 

Assessment Team, 2000). The present 

report includes the recent oil and gas 

assessment of geologic provinces north of 

the Arctic Circle (U.S. Geological Survey 

Circum-Arctic Resource Appraisal 

Assessment Team, 2008). However, not 

all potential oil- and gas-bearing provinces of the world were assessed in the 

present study.

The methodology for the assessment 

included a complete geologic framework 

description for each province based mainly 

on published literature, and the definition

of petroleum systems and assessment units 

(AU) within these systems. In this study, 

313 AUs were defined and assessed for

undiscovered oil and gas accumulations. 

Exploration and discovery history was a 

critical part of the methodology to determine sizes and numbers of undiscovered 

accumulations. In those AUs with few or 

no discoveries, geologic and production 

analogs were used as a partial guide to 

estimate sizes and numbers of undiscovered oil and gas accumulations, using a 

database developed by the USGS following the 2000 assessment (Charpentier and 

others, 2008). Each AU was assessed for 

undiscovered oil and nonassociated gas 

accumulations, and co-product ratios were 

used to calculate the volumes of associated gas (gas in oil fields) and volumes of

natural gas liquids. This assessment is for 

conventional oil and gas resources only; 

unconventional resource assessments 

(heavy oil, tar sands, shale gas, shale oil, 

tight gas, coalbed gas) for priority areas 

of the world are being completed in an 

ongoing but separate USGS study.

Resource Summary

The USGS assessed undiscovered 

conventional oil and gas resources in 

313 AUs within 171 geologic provinces. In 

this report the results are presented by geographic region, which correspond to the 

eight regions used by the U.S. Geological 

Survey World Energy Assessment Team 

(2000) (table 1). For undiscovered, 

technically recoverable resources, the 

mean totals for the world are as follows: (1) 565,298 million barrels of oil 

(MMBO); (2) 5,605,626 billion cubic feet 

of gas (BCFG); and (3) 166,668 million 

barrels (MMBNGL) of natural gas liquids. 

The ranges of resource estimates (between 

the 95 and 5 fractiles) reflect the geologic

uncertainty in the assessment process 

(table 1). The assessment results indicate 

that about 75 percent of the undiscovered 

conventional oil of the world is in four 

Using a geology-based assessment methodology, 

the U.S. Geological Survey estimated means of 

565 billion barrels of conventional oil and 5,606 trillion cubic feet of undiscovered conventional natural 

gas in 171 priority geologic provinces of the world, 

exclusive of the United States.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3028

March 2012

World Petroleum Resources Project

An Estimate of Undiscovered Conventional 

Oil and Gas Resources 

of the World, 2012

Eolian dunes of the An Nefud sand sea, northern Saudi Arabia. (Photograph by C.J. Schenk, 

U.S. Geological Survey.)
Assessed provinces

0 1,500 3,000 MILES EXPLANATION

0 1,500 3,000 KILOMETERS

Region 5

North America

Region 6

South America and Caribbean

Region 3

Asia and

Pacific

Region 8

South Asia

Region 1

Former 

Soviet Union

Region 2

Middle East and

North Africa

Region 7

sub-Saharan

Africa

Region 4

Europe

Region 5

North America

Region 1

Former 

Soviet Union

Region 3

Asia and

Pacific

Region 1

Former 

Soviet Union

Region 2

Middle East and

North Africa

Region 7

sub-Saharan

Africa

Region 4

Europe

Region 6

South America and Caribbean

Region 8

South Asia

ARCTIC

CIRCLE

ARCTIC

Polar Projection

CIRCLE

0°

90°W 90°E

180°

ARCTIC

CIRCLE

North

Pole

Circum-Arctic

Region

5

Region

1

Region

0

Region

4

180° 170° 160° 150° 140° 130° 120° 110° 100° 90° 80° 70° 60° 50° 40° 30° 20° 10° 0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 100° 110° 120° 130° 140° 150° 160° 170° 180°

90°

80°

70°

60°

50°

40°

30°

20°

10°

0°

10°

20°

30°

40°

50°

60°

70°

80°

90°

Inset

map

Figure 1. Locations of 171 geologic provinces (red areas) of the world assessed in this study. Inset map shows assessed provinces of the Arctic in a polar projection; Arctic is defined as provinces above the Arctic Circle (yellow line). Arctic provinces are included in Regions 0, 1, 4, and 5.
Regions Field

type

Total undiscovered resources

Oil (MMBO) Gas (BCFG) NGL (MMBNGL)

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

0. Arctic Ocean Oil 15,984 45,559 177,175 66,211 54,892 178,640 606,787 237,485 2,083 6,487 19,754 8,193

1. Former Soviet Union Gas 343,396 1,058,432 3,448,972 1,385,046 8,009 25,058 76,955 31,786

2. Middle East and North Africa

Oil 43,316 101,406 212,678 111,201 49,194 124,226 308,443 144,787 1,578 4,026 10,389 4,764

Gas 334,063 729,200 1,490,538 796,513 10,363 23,220 50,605 25,912

3. Asia and Pacific

Oil 20,950 43,607 87,744 47,544 52,579 117,354 253,416 130,483 1,173 2,742 6,346 3,125

Gas 269,523 562,461 1,110,663 607,845 7,517 16,340 33,736 17,917

4. Europe

Oil 4,344 8,561 19,417 9,868 6,605 16,422 50,460 21,171 245 570 1,616 710

Gas 54,072 109,589 249,678 127,454 912 1,924 4,401 2,219

5. North America

Oil 25,500 62,618 208,032 83,386 42,498 112,675 398,902 152,847 879 2,685 11,923 4,103

Gas 117,885 300,810 1,111,423 420,890 2,910 10,489 43,785 15,164

6. South America and Caribbean

Oil 44,556 108,098 261,862 125,900 99,532 246,922 637,661 295,475 2,909 7,570 20,048 9,119

Gas 130,015 324,762 838,345 383,062 3,941 9,937 26,532 11,882

7. sub-Saharan Africa

Oil 40,777 102,961 232,090 115,333 40,553 104,711 262,898 122,188 1,237 3,394 9,237 4,089

Gas 278,230 557,579 1,190,770 621,341 9,425 20,584 49,935 23,879

8. South Asia

Oil 3,323 5,575 9,339 5,855 8,404 14,648 25,087 15,419 189 337 586 356

Gas 68,651 134,622 250,144 143,620 1,623 3,197 6,155 3,450

Total conventional resources 565,298 5,605,626 166,668

regions: (1) South America and Caribbean, 

(2) sub-Saharan Africa, (3) Middle East 

and North Africa, and (4) the Arctic 

provinces portion of North America. 

Significant undiscovered conventional

gas resources remain in all of the world’s 

regions (table 1).

Regions 0 and 1 (29 assessed provinces) encompass geologic provinces 

within countries of the former Soviet 

Union and include many provinces of the 

Arctic (fig. 1). Of the mean undiscovered estimate of 66 billion barrels of oil 

(BBO) in this region, about 43 percent 

is estimated to be in Arctic provinces. 

This region also contains significant gas

resources [mean of 1,623 trillion cubic feet 

of gas (TCFG)], about 58 percent of which 

is estimated to be in three Arctic AUs: 

South Kara Sea AU (622 TCFG); South 

Barents Basin AU (187 TCFG), and North 

Barents Basin AU (127 TCFG).

Region 2 (26 assessed provinces), 

the Middle East and North Africa, includes 

the Zagros Fold Belt of Iran, Arabian 

Peninsula, southern Turkey, and geologic 

provinces of North Africa from Egypt to 

Morocco. This region is estimated to contain a mean of 111 BBO, about 60 percent 

(65 BBO) of which is estimated to be 

in the Zagros and Mesopotamian provinces. This region is estimated to contain 

a conventional gas resource mean of 

941 TCFG, about 60 percent (566 TCFG) 

of which is estimated to be in the Zagros 

Fold Belt and the offshore areas of the 

Red Sea Basin, Levantine Basin, and Nile 

Delta provinces.

Region 3 (39 assessed provinces), 

Asia and Pacific, includes geologic

provinces of China, Vietnam, Thailand, 

Malaysia, Cambodia, Philippines, Brunei, 

Indonesia, Papua New Guinea, East 

Timor, Australia, and New Zealand. Of 

the total mean undiscovered oil resources 

of 48 BBO, about 33 percent is estimated 

to be in China provinces (15.7 BBO), 

and 10 percent is in Australian provinces 

(5 BBO). Other significant oil resources

are in offshore Brunei (3.6 BBO), Kutei 

Basin (3 BBO), and South China Sea 

(2.5 BBO) provinces. Of the undiscovered mean total of 738 TCFG, about 

45 percent (335 TCFG) is in provinces 

of Australia (227 TCFG) and China 

(108 TCFG). The rest of the gas resource 

is distributed across the other provinces 

of Southeast Asia.

Table 1. Assessment results for mean, undiscovered, technically recoverable oil, gas, and natural gas liquids for provinces of the 

world by region.

[MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates. For gas 

accumulations, all liquids are included as NGL (natural gas liquids). Total undiscovered gas resources are the sum of nonassociated and associated gas. F95 represents a 

95-percent chance of at least the amount tabulated; other fractiles are defined similarly. Field type: Oil―oil, associated gas, and NGL in oil fields; Gas―nonassociated

gas and liquids in gas fields. Gray shading indicates not applicable]
Vertical limestone beds forming cliffs along Three Pagodas Fault Zone, near Hua Hin, 

Thailand. (Photograph by C.J. Schenk, U.S. Geological Survey.)

Region 4 (6 assessed provinces) 

includes Europe and several Arctic 

provinces. Of the mean of 9.9 BBO 

of undiscovered oil, about 50 percent 

(5 BBO) is estimated to be in the North 

Sea province. Of the undiscovered 

gas resource of 149 TCFG, the Arctic 

provinces are estimated to contain about 

40 percent (58 TCFG). Significant

undiscovered gas resources are estimated to be in the Norwegian continental margin, Provencal Basin, and 

Po Basin provinces.

Region 5 (21 assessed provinces), 

North America exclusive of the United 

States, includes Mexico, Canada, 

and several Arctic provinces. Of the 

mean oil resource of 83 BBO, about 

75 percent (61 BBO) is estimated to 

be in Arctic provinces, and 23 percent (19 BBO) is estimated to be in 

Mexican Gulf provinces. In this region 

about 83 percent (459 TCFG) of the 

undiscovered conventional gas is in the 

Arctic provinces.

Region 6 (31 assessed provinces) 

includes South America and the 

Caribbean area. Of the mean estimate of 126 BBO in this region, about 

44 percent (55.6 BBO) is estimated to 

be in offshore subsalt reservoirs in the 

Santos, Campos, and Espirito Santo 

basin provinces. Other significant mean

oil resources are estimated to be in the 

Guyana−Suriname Basin (12 BBO),

Santos Basin (11 BBO), Falklands 

(5.3 BBO), and Campos Basin (3.7 BBO) 

provinces. Undiscovered gas resources 

are less concentrated and are distributed 

among many provinces.

Region 7 (13 assessed provinces), 

sub-Saharan Africa, is estimated to 

contain a mean 115 BBO, of which 

about 75 percent is estimated to be in 

coastal provinces related to the opening 

of the Atlantic Ocean, such as Senegal, 

Gulf of Guinea, West African Coastal, 

and West-Central Coastal provinces. 

Of the undiscovered gas resource mean 

of 744 TCFG, more than half is estimated to be in provinces of offshore 

east Africa, including those offshore 

Tanzania, Mozambique, Madagascar, 

and Seychelles.

Region 8 (6 assessed provinces), 

South Asia, includes India, Pakistan, 

Afghanistan, Bangladesh, and Burma. 

Of the mean of 5.9 BBO, about 1.8 BBO 

is estimated to be in the Central Burma 

Basin province and 1.4 BBO is in the 

Bombay province. Of the undiscovered 

gas resource of 159 TCFG, about 39 percent (62 TCFG) of the undiscovered 

gas resource is in the three provinces of 

offshore eastern India.

Although unconventional oil and 

gas resources, such as heavy oil, tar 

sands, shale gas, shale oil, tight gas, 

and coalbed gas, are not included in this 

study, unconventional resource volumes 

can be truly significant. For example, the

mean estimate for recoverable heavy oil 

from the Orinoco Oil Belt in Venezuela 

alone is 513 BBO (U.S. Geological 

Survey Orinoco Oil Belt Assessment 

Team, 2009), compared to mean conventional resources of 565 BBO for 

171 provinces reported in this study.

References Cited

Charpentier, R.R., Klett, T.R., and 

Attanasi, E.D., 2008, Database for 

assessment–unit analogs (exclusive 

of the United States), Version 1.0: 

U.S. Geological Survey Open-File 

Report 2007−1404, 36 p.

U.S. Geological Survey World Energy 

Assessment Team, 2000, U.S. Geological Survey world petroleum 

assessment 2000—Description and 

results: U.S. Geological Survey Digital 

Data Series DDS−60, 4 CD-ROMs.

U.S. Geological Survey Circum-Arctic 

Resource Appraisal Assessment 

Team, 2008, Circum-Arctic resource 

appraisal: Estimates of undiscovered oil and gas north of the Arctic 

Circle: U.S. Geological Survey Fact 

Sheet 2008−3049, 4 p.

U.S. Geological Survey Orinoco Oil 

Belt Assessment Team, 2009, An 

estimate of recoverable heavy oil 

resources of the Orinoco Oil Belt, 

Venezuela: U.S. Geological Survey 

Fact Sheet 2009−3028, 4 p.
1

2 3

For Further Information

Supporting studies of the geologic models and the methodology used in the 

assessment of priority world provinces are in progress. Assessment results are 

available at the USGS Energy Program website, http://energy.cr.usgs.gov/oilgas/.

Contact: Christopher J. Schenk, Task Leader (schenk@usgs.gov), 

U.S. Geological Survey, MS 939, Box 25046, Denver, Colorado, USA 80225

World Conventional Resources Assessment Team

(in alphabetical order)

Michael E. Brownfield, Ronald R. Charpentier, Troy A. Cook, Donald L. Gautier, 

Debra K. Higley, Mark A. Kirschbaum, Timothy R. Klett, Janet K. Pitman, 

Richard M. Pollastro, Christopher J. Schenk (Task Leader),

Marilyn E. Tennyson, Craig J. Wandrey, and Katherine J. Whidden.

1, Icebergs immediately offshore from Ilulissat, Greenland; 2, Snowy peaks and muddy tidal flats of Cook Inlet, south 

of Anchorage, Alaska; and 3, Valley of the Atigun River with the Trans-Alaska Pipeline near Galbraith, Alaska. 

(Photographs by C.J. Schenk, U.S. Geological Survey.)