World Petroleum Resources Project

Assessment of Undiscovered Conventional Oil and Gas 

Resources of the Arabian Peninsula and Zagros Fold Belt, 

2012

Using a geology-based assessment methodology, the U.S. Geological Survey estimated means 

of 86 billion barrels of oil and 336 trillion cubic feet of undiscovered natural gas resources in 

the Arabian Peninsula and Zagros Fold Belt.

Introduction

The U.S. Geological Survey (USGS) assessed 

the potential for undiscovered conventional oil and 

gas accumulations within the Arabian Peninsula and 

Zagros Fold Belt as part of the USGS World Petroleum Resources Project. Twenty-three assessment 

units within seven petroleum systems were quantitatively assessed in this study, which represents a 

reassessment of this area last published in 2000 (U.S. 

Geological Survey World Energy Assessment Team, 

2000) (fig. 1).

The methodology for the assessment included 

geologic definitions of total petroleum systems (TPS) 

and assessment units (AU) within these systems. 

Exploration and discovery history was a critical part 

of the methodology used to estimate sizes and numbers of undiscovered conventional accumulations. 

Each AU was assessed for undiscovered oil and nonassociated gas accumulations, and coproduct ratios 

were used to calculate the volumes of associated gas 

(gas in oil fields) and volumes of natural gas liquids.

Total Petroleum Systems

The seven TPSs and the main geologic elements used to define them are as follows: (1) Huqf–

Paleozoic TPS―petroleum generated from Precambrian–Cambrian shales of the Huqf Supergroup in 

three Oman basins; (2) Paleozoic Composite TPS―

petroleum generated from Silurian (and possibly 

Ordovician) marine source rocks over much of the 

Arabian Peninsula; (3) Paleozoic–Mesozoic Composite TPS includes the Euphrates Graben of Syria in 

which petroleum from Triassic source rock is present 

in addition to that from Paleozoic source rocks; 

(4) Mesozoic Composite TPS―petroleum generated from synrift Triassic and other Mesozoic source 

rocks in the Palmyra and Sinjar areas; (5) Madbi–

Amran–Qishn TPS of Yemen―petroleum generated 

from Upper Jurassic marine source rocks; (6) Middle 

Cretaceous Natih TPS―petroleum from the Natih 

Formation trapped in the Fahud Salt Basin of Oman; 

and (7) Mesozoic–Cenozoic Composite TPS―

petroleum generated from Middle and Upper Jurassic and Lower and Upper Cretaceous source marine 

rocks over a wide area of the eastern Arabian Peninsula and Zagros. The 23 AUs that were defined 

geologically and assessed within these TPS are listed 

in table 1.

Resource Summary

The USGS assessed undiscovered conventional 

oil and gas resources in 23 AUs within seven petroleum systems, with the following estimated mean 

totals: (1) for conventional oil resources, 85,856 

million barrels of oil (MMBO), with a range from 

34,006 to 161,651 MMBO; (2) for undiscovered 

conventional gas, 336,194 billion cubic feet of gas 

(BCFG), with a range from 131,488 to 657,939 

BCFG; and (3) for natural gas liquids (NGL), 11,972 

MMBNGL, with a range from 4,513 to 24,788 

MMBNGL (table 1).

Of the mean undiscovered conventional oil 

resource of 85,856 MMBO, about 92 percent (78,747 

MMBO) is estimated to be in six AUs within the 

Mesozoic–Cenozoic Composite Total Petroleum 

System (fig. 1B); most of this oil is estimated to 

be in the Zagros Fold Belt Structures AU (mean of 

38,464 MMBO), the Mesopotamian Basin Anticlines 

AU (mean of 26,856 MMBO), the Arabian Platform 

Printed on recycled paper U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3115

September 2012
Figure 1. A. Locations of Huqf–Paleozoic Total Petroleum System (TPS), Paleozoic Composite TPS, Paleozoic–Mesozoic Composite TPS, 

and Mesozoic Composite TPS and associated assessment units (AU) of the Arabian Peninsula and Zagros Fold Belt. B. Locations of the 

Madbi–Amran–Qishn TPS, Middle Cretaceous Natih TPS, and Mesozoic–Cenozoic Composite TPS and associated AUs of the Arabian 

Peninsula and Zagros Fold Belt.

!

! !

Sanaa

SAUDI ARABIA

EGYPT

JORDAN

IRAQ

SYRIA

TURKEY

TURKMENISTAN

IRAN

U.A.E. OMAN

YEMEN

ETHIOPIA

SUDAN

ERITREA

CASPIAN 

SEA

ARABIAN 

GULF

RED SEA

ARABIAN SEA

MEDITERRANEAN SEA

A

35° 40° 45° 50° 55°

35°

30°

25°

20°

15°

Southeast Turkey Thrust Zone Reservoirs 

Aleppo Platform Reservoirs Sinjar 

Reservoirs 

Northwest Gulf

Salt Basin

Reservoirs

Central Arabia

Paleozoic

Reservoirs

Butabul–Ghudun Fold Belt

Reservoirs

South Oman 

Salt Basin Reservoirs

Rub Al Khali Paleozoic Reservoirs

Qatar 

Arch

Platform

Reservoirs

South Gulf

Salt Basin

Reservoirs

Ghaba– Fahud

Salt Basin

Reservoirs

Euphrates

 Graben

 Reservoirs

Northern Arabia Paleozoic Reservoirs Zagros Fold Belt Paleozoic Reservoirs 

Palmyra Fold Belt Reservoirs 

Total Petroleum Systems

Paleozoic Composite 

Huqf-Paleozoic

Paleozoic-Mesozoic Composite

Mesozoic Composite

EXPLANATION

Explanation

Assessment units

!

! !

Sanaa

SAUDI ARABIA

EGYPT

JORDAN

IRAQ

SYRIA

TURKEY

TURKMENISTAN

IRAN

U.A.E. OMAN

YEMEN

ETHIOPIA

SUDAN

ERITREA

CASPIAN 

SEA

RED SEA

ARABIAN SEA

35°

30°

25°

20°

15°

B

ARABIAN SEA

Arabian 

Platform 

Structures

Mesopotamian Basin 

 Anticlines

Zagros

Fold Belt

Structures

Horst Block and

Suprasalt Structural Oil South Gulf Suprasalt Structures and

 Desert Anticlines

South 

Gulf 

Basin

and

 Oman 

 Foreland

Structures

Natih-Wasia

 

Ma’Rib-Al Jawf/

Shabwah/

Masila Grabens

Total Petroleum Systems

Mesozoic-Cenozoic Composite 

Madbi-Amran-Qishn

Middle Cretaceous Natih

EXPLANATION

MEDITERRANEAN SEA

SUDAN

ERITREA

RED SEA

Area

of Mideast

Assessment

IRAN

SUDAN

SAUDI ARABIA

RUSSIA KAZAKHSTAN

TURKEY

IRAQ

ETHIOPIA

EGYPT

YEMEN

UKRAINE

TURKMENISTAN

SYRIA

SOMALIA

0 275 KILOMETERS

0 275 MILES

ARABIAN 

GULF

Stratigraphic

Structural/

Assessment units

Assessment units
Total petroleum systems 

(TPS) 

and assessment units (AU)

AU

probability

Field 

type

Expected

largest 

field size

Total undiscovered resources

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

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

Huqf-Paleozoic TPS (in 2 provinces)

South Oman Salt Basin 

Reservoirs AU 1.0

 Oil 54 212 360 578 373 159 280 475 294 20 34 59 36

 Gas 200 48 195 996 315 1 6 31 10

Ghaba-Fahud Salt Basin 

Reservoirs AU 1.0

 Oil 16 156 233 344 240 84 129 193 132 3 5 9 6

 Gas 760 2,711 4,743 7,788 4,927 117 213 383 227

Butabul-Ghudun Fold Belt 

Reservoirs AU 1.0

 Oil 11 124 185 271 189 520 790 1,172 810 6 9 14 9

 Gas 220 119 348 1,191 458 4 11 37 14

Paleozoic Composite TPS (in 6 provinces)

Rub al Khali Paleozoic 

Reservoirs AU 1.0

 Oil 144 104 293 826 355 133 380 1,081 464 7 20 58 24

 Gas 2,443 9,445 19,030 35,836 20,361 592 1,213 2,301 1,300

South Gulf Salt Basin 

Reservoirs AU 1.0

 Oil 145 105 297 830 359 327 962 2,828 1,189 13 40 123 51

 Gas 2,295 7,828 16,050 30,390 17,171 319 659 1,248 705

Central Arabia Paleozoic 

Reservoirs AU 1.0

 Oil 189 225 528 1,218 599 290 686 1,610 783 15 36 86 41

 Gas 988 1,309 2,976 6,599 3,336 81 188 432 213

Northwest Gulf Salt Basin 

Reservoirs AU 1.0

 Oil 145 105 297 830 359 326 965 2,825 1,191 13 40 123 51

 Gas 1,904 4,525 9,971 19,626 10,733 184 408 809 441

Qatar Arch Paleozoic 

Reservoirs AU 1.0

 Oil 0 0 0 0 0 0 0 0 0 0 0 0

 Gas 427 47 232 1,963 536 1 7 62 17

Northern Arabia Paleozoic 

Reservoirs AU 1.0

 Oil 252 413 975 2,064 1,072 533 1,268 2,720 1,400 28 66 146 74

 Gas 2,669 12,239 24,165 44,995 25,769 774 1,541 2,893 1,645

Zagros Fold Belt Reservoirs 

AU 1.0

 Oil 102 469 909 1,672 968 1,105 2,245 4,265 2,408 16 33 63 35

 Gas 19,766 40,736 95,892 194,610 103,772 686 1,626 3,382 1,776

Southeast Turkey Thrust 

Zone Reservoirs AU 1.0

 Oil 17 289 427 624 438 16 24 36 25 1 2 3 2

 Gas 38 72 125 236 135 4 6 13 7

Paleozoic-Mesozoic Composite TPS (in 1 province)

Euphrates Graben 

Reservoirs AU 1.0

 Oil 22 96 157 246 162 79 131 208 135 8 13 21 14

 Gas 54 113 199 345 210 5 9 16 10

Mesozoic Composite TPS (in 3 provinces)

Sinjar Reservoirs AU 1.0

 Oil 16 83 131 201 135 300 485 756 501 15 25 39 26

 Gas 48 257 374 531 381 6 10 14 10

Aleppo Platform Reservoirs 

AU 1.0

 Oil 10 102 153 226 157 221 338 504 347 5 7 11 8

 Gas 0 0 0 0 0 0 0 0

Palmyra Fold Belt 

Reservoirs AU 1.0

 Oil 29 222 342 511 351 12 19 30 20 1 1 2 1

 Gas 387 1,674 2,804 4,464 2,903 87 147 236 152

Madbi-Amran-Qishn TPS (in 1 province)

Ma ‘Rib-Al Jawf/Shabwah/

Masila Grabens AU 1.0

 Oil 121 595 1,049 1,773 1,098 95 246 644 293 3 7 18 8

 Gas 282 1,052 1,858 3,168 1,949 25 46 80 48

Middle Cretaceous Natih TPS (in 1 province)

Natih-Wasia Structural/

Stratigraphic AU 1.0

 Oil 10 132 239 429 254 180 348 638 370 3 7 13 7

 Gas 0 0 0 0 0 0 0 0

Mesozoic-Cenozoic Composite TPS (in 5 provinces)

South Gulf Suprasalt 

Structures and Desert 

Anticlines AU

1.0

 Oil 116 553 986 1,682 1,034 634 1,241 2,324 1,328 20 41 82 45

 Gas 878 1,953 4,570 9,863 5,063 126 302 662 336

South Gulf Basin and Oman 

Foreland Structures AU 1.0

 Oil 46 262 446 744 467 181 359 708 391 12 24 48 26

 Gas 245 1,536 2,589 4,284 2,709 94 161 268 168

Horst Block and Suprasalt 

Structural Oil AU 1.0

 Oil 643 2,529 4,985 9,163 5,300 1,792 3,580 6,662 3,820 48 97 183 104

 Gas 0 0 0 0 0 0 0 0

Arabian Platform Structures 

AU 1.0

 Oil 524 3,228 6,220 11,430 6,626 1,630 3,141 5,774 3,347 55 107 199 115

 Gas 0 0 0 0 0 0 0 0

Mesopotamian Basin 

Anticlines AU 1.0

 Oil 5,715 9,985 24,737 51,257 26,856 8,359 22,679 57,504 26,467 274 759 2,016 905

 Gas 3,203 208 1,493 16,751 4,141 31 226 2,542 629

Zagros Fold Belt Structures 

AU 1.0

 Oil 10,297 14,017 34,944 74,732 38,464 17,734 48,072 128,317 57,608 545 1,484 4,054 1,791

Gas 6,130 10,906 25,681 53,029 28,002 265 725 2,009 885

Total conventional

 resources 34,006 78,893 161,651 85,856 131,488 301,663 657,939 336,194 4,513 10,361 24,788 11,972

Table 1. Assessment results for undiscovered conventional oil and gas resources of the Arabian Peninsula and Zagros Fold Belt.

[Largest expected mean field size in million barrels of oil and billion cubic feet of gas. 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). Undiscovered gas resources 

are the sum of nonassociated (gas in gas fields) and associated gas (gas in oil fields). F95 represents 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. AU, assessment unit; AU probability is the chance of at least one accumulation of 

minimum size within the AU. NGL, natural gas liquids. TPS, total petroleum system. Gray shading indicates not applicable]
Structures AU (mean of 6,626 MMBO), and the 

Horst Block and Suprasalt Structural Oil AU (mean 

of 5,300 MMBO).

For the undiscovered conventional gas resource 

mean of 336,194 BCFG, 96 percent is in two total 

petroleum systems: Paleozoic Composite TPS 

(mean of 189,273 BCFG) and the Mesozoic–

Cenozoic Composite TPS (mean of 132,876 BCFG). 

In the Paleozoic Composite TPS, 56 percent (106,180 

BCFG) of the undiscovered gas is estimated to be 

in the Zagros Fold Belt Reservoirs AU (table 1). 

Similarly, 64 percent (85,610 BCFG) of the undiscovered gas in the Mesozoic–Cenozoic Composite 

TPS is in the Zagros Fold Belt Structures AU.

Reference Cited

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.

Arabian Peninsula and Zagros Fold Belt Assessment Team

Janet K. Pitman, Christopher J. Schenk, Michael E. Brownfield, 

Ronald R. Charpentier, Troy A. Cook, Timothy R. Klett, and Richard M. 

Pollastro.

For Further Information

Supporting studies of the geologic models and the methodology 

used in the assessment of Arabian Peninsula and Zagros Fold Belt 

provinces are in progress. Assessment results are available at the 

USGS Energy Program website, http://energy.usgs.gov/.