U.S. Department of the Interior

U.S. Geological Survey

National Assessment of Oil and Gas Fact Sheet

Assessment of Undiscovered Oil and Gas Resources in 

Tertiary Strata of the Gulf Coast, 2007

Printed on recycled paper

Introduction

The U.S. Geological Survey (USGS) recently completed 

an assessment of the undiscovered oil and gas resources in 

Tertiary strata and coalbed gas resources in Cretaceous-Tertiary 

strata of the onshore areas and State waters of the Gulf Coast 

Figure 1. Map showing the part of the Upper Jurassic-Cretaceous-Tertiary Composite Total Petroleum System that is 

onshore and in State waters of the Gulf Coast of the United States (blue line). Province boundaries defined by the U.S. 

Geological Survey are indicated by red outlines.

Using a geology-based assessment methodology, 

the U.S. Geological Survey estimated a mean of 113.7 

trillion cubic feet of undiscovered natural gas, a mean of 

690 million barrels of undiscovered oil, and a mean of 

3.7 billion barrels of undiscovered natural gas liquids in 

onshore lands and State waters of the Gulf Coast.

(fig. 1). The assessment is based on geologic elements of a 

total petroleum system (TPS), including characterization of 

hydrocarbon source rocks (source-rock maturation, hydrocarbon 

generation and migration), reservoir rocks (sequence 

stratigraphy and petrophysical properties), and hydrocarbon 

traps (trap formation, timing, and seals). Using these criteria, 

the USGS defined an Upper Jurassic-Cretaceous-Tertiary 

Composite TPS for conventional oil and gas resources that 

extends around the entire Gulf of Mexico, including portions 

of both the United States and Mexico. However, the present 

assessment of undiscovered conventional oil and gas resources 

includes only that portion of the TPS that lies onshore and in 

State waters of the United States (fig. 1). In addition, the USGS 

defined three self-sourced coalbed gas TPSs. Two are entirely 

Western Gulf 47

East 

Texas 

Basin 

48 Louisiana-Mississippi 

Salt Basins 49

Florida 

Peninsula

50

Miami

Tampa

Austin

Dallas

Houston

Atlanta

Memphis

Wichita

Raleigh Nashville

Charlotte

Fort Worth

Birmingham

Louisville

San Antonio

New Orleans

Saint Louis

Oklahoma City

Corpus Christi

TEXAS

FLORIDA

GEORGIA

OKLAHOMA

KANSAS

ALABAMA

LOUISIANA

SOUTH CAROLINA

COLORADO

MISSISSIPPI

ARKANSAS

MISSOURI

ILLINOIS

TENNESSEE

KENTUCKY

NORTH CAROLINA

VIRGINIA

MEXICO

UNITED

STATES

Gulf of Mexico

Atlantic

Ocean

 104° 102° 100° 98° 96° 94° 92° 90° 88° 86° 84° 82° 80° 78°

24°

26°

28°

30°

32°

34°

36°

38°

0 50 100 200 MILES

Fact Sheet 2007–3066

August 2007
Total Petroleum Systems 

(TPS) 

and Assessment Units (AU)

Field 

Type

Total Undiscovered Resources

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

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

Upper Jurassic-Cretaceous-Tertiary Composite TPS (504701)

Wilcox Stable Shelf Oil 

and Gas AU (50470116)

Oil 12 49 111 54 8 33 83 38 0 1 3 1

Gas 117 403 846 434 4 13 30 14

Wilcox Expanded Fault Zone 

Gas and Oil AU (50470117)

Oil 18 49 95 52 74 215 459 234 2 6 14 7

Gas 714 2,114 4,299 2,264 20 61 136 68

Wilcox Slope and Basin Floor 

Gas AU (50470118)

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

Gas 5,173 23,629 56,486 26,398 78 366 959 423

Wilcox-Lobo Slide Block Gas 

AU (50470119)

Oil 1 4 9 4 6 20 48 23 0 0 1 1

Gas 1,543 6,803 15,732 7,498 24 109 276 125

Lower Claiborne Stable Shelf 

Gas and Oil AU (50470120)

Oil 3 7 13 7 7 19 40 21 0 0 1 0

Gas 21 63 124 67 0 2 3 2

Lower Claiborne Expanded 

Fault Zone Gas AU (50470121)

Oil 1 3 8 4 6 16 43 19 0 1 3 1

Gas 351 942 1,767 987 13 37 76 39

Lower Claiborne Slope and 

Basin Floor Gas AU (50470122)

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

Gas 573 3,195 8,044 3,620 21 124 338 145

Lower Claiborne Cane River 

AU (50470123)

Oil

Gas

Upper Claiborne Stable Shelf 

Gas and Oil AU (50470124)

Oil 4 12 23 13 12 36 78 40 0 1 2 1

Gas 97 357 858 402 3 10 25 11

Upper Claiborne Expanded 

Fault Zone Gas AU (50470125)

Oil 8 26 53 28 39 128 287 142 3 9 21 10

Gas 1,417 4,386 9,096 4,740 95 307 698 341

Upper Claiborne Slope and 

Basin Floor Gas AU (50470126)

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

Gas 1,706 8,147 19,632 9,107 116 569 1,489 655

Jackson Stable Shelf Oil and 

Gas AU (50470127)

Oil 2 4 10 5 2 6 16 7 0 0 0 0

Gas 7 16 32 17 0 0 1 1

Jackson Expanded Fault Zone 

Gas and Oil AU (50470128)

Oil 5 17 40 19 7 26 66 30 0 1 3 1

Gas 110 449 1,036 495 4 16 39 18

Jackson Slope and Basin Floor 

Gas AU (50470129)

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

Gas 94 393 929 438 3 15 39 18

Jackson Louisiana-MississippiAlabama Area AU (50470130)

Oil

Gas

Vicksburg Stable Shelf Oil and 

Gas AU (50470131)

Oil 5 16 35 17 18 61 147 69 0 1 4 2

Gas 39 114 218 120 1 3 5 3

Vicksburg Expanded Fault Zone 

Gas and Oil AU (50470132)

Oil 6 19 41 21 17 58 133 65 1 3 7 3

Gas 2,057 8,598 19,880 9,511 68 295 747 336

Vicksburg Slope and Basin 

Floor Gas AU (50470133)

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

Gas 1,607 6,920 15,840 7,621 61 269 668 305

Vicksburg Mississippi-Alabama 

Area AU (50470134)

Oil

Gas

Frio Stable Shelf Oil and Gas 

AU (50470135)

Oil 2 5 11 5 7 22 52 25 0 0 1 0

Gas 88 227 437 241 2 5 11 6

Frio Expanded Fault Zone Oil 

and Gas AU (50470136)

Oil 4 14 30 16 24 82 186 90 1 2 5 2

Gas 509 1,265 2,292 1,321 13 34 68 36

Conventional Oil and Gas Resources

[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). 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. TPS, total petroleum system; AU, assessment unit. Gray shading 

indicates not applicable]

Table 1. Gulf Coast assessment results.

Not quantitatively assessed

Not quantitatively assessed

Not quantitatively assessed
Total Petroleum Systems 

(TPS) 

and Assessment Units (AU)

Field 

Type

Total Undiscovered Resources

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

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

Upper Jurassic-Cretaceous-Tertiary Composite TPS (504701)—Continued

Frio Slope and Basin Floor Gas 

AU (50470137)

Oil 28 102 220 110 84 320 756 358 2 9 24 11

Gas 1,271 4,829 10,397 5,231 81 322 757 358

Anahuac Oil and Gas 

AU (50470138)

Oil 3 13 39 16 8 33 103 41 0 1 2 1

Gas 62 240 578 270 2 7 17 8

Hackberry Oil and Gas 

AU (50470139)

Oil 6 22 52 25 17 69 178 80 0 2 6 2

Gas 539 1,632 3,187 1,727 34 109 233 118

Lower Miocene Shelf Oil and 

Gas AU (50470140)

Oil 4 15 40 17 9 34 99 42 0 0 1 1

Gas 82 301 641 324 1 5 11 5

Lower Miocene Slope and 

Basin Gas AU (50470141)

Oil 5 16 37 18 20 74 181 84 1 2 6 3

Gas 5,786 17,582 37,327 19,116 137 445 1,027 496

Middle Miocene Shelf Oil and 

Gas AU (50470142)

Oil 5 21 56 25 21 92 263 110 0 2 6 2

Gas 673 3,000 7,040 3,321 12 54 140 62

Middle Miocene Slope and 

Basin Gas AU (50470143)

Oil 25 115 315 135 75 358 1,040 432 2 8 26 10

Gas 277 1,242 3,081 1,405 7 30 81 35

Upper Miocene Shelf Oil and 

Gas AU (50470144)

Oil 7 28 70 32 9 40 108 47 0 1 1 1

Gas 101 441 1,077 498 3 13 33 15

Upper Miocene Slope and 

Basin Gas AU (50470145)

Oil 8 33 88 38 40 168 483 203 1 5 16 6

Gas 41 144 320 158 2 8 20 9

Plio-Pleistocene Shelf Oil and 

Gas AU (50470146)

Oil 7 26 62 29 9 37 95 43 0 0 1 1

Gas 21 70 154 77 1 4 10 5

Wilcox Mississippi Embayment 

AU (50470147)

Oil

Gas

Frio Basin Margin 

AU (50470148)

Oil

Gas

Total Conventional

 Resources 169 616 1,458 690 25,595 99,449 226,294 109,651 819 3,287 8,091 3,724

Olmos Coalbed Gas TPS (504702)

Cretaceous Olmos Coalbed Gas 

AU (50470281) CBG 37 70 133 75 0 0 1 0

Rio Escondido Basin Olmos 

Coalbed Gas AU (53000281) CBG 60 114 215 123 0 0 1 0

Wilcox Coalbed Gas TPS (504703)

Wilcox Coalbed Gas

AU (50470381) CBG 1,565 3,442 7,570 3,861 0 0 0 0

Cretaceous-Tertiary Coalbed Gas TPS (504704)

Cretaceous-Tertiary Coalbed 

Gas AU (50470481) CBG

Total Continuous 

 Resources 1,662 3,626 7,918 4,059 0 0 2 0

Total Undiscovered 

 Oil and Gas Resources 169 616 1,458 690 27,257 103,075 234,212 113,710 819 3,287 8,093 3,724

Conventional Oil and Gas Resources Continuous Oil and Gas Resources

Table 1. Gulf Coast assessment results.—Continued

Not quantitatively assessed

Not quantitatively assessed

Not quantitatively assessed
within the United States, and the third has one assessment unit 

(AU) in the United States and one AU in Mexico. The portion 

of the composite conventional TPS that lies within the United 

States covers a geographic area that extends from the southwest 

boundary of the Western Gulf Province on the Texas-Mexico 

border eastward into Texas and Louisiana, including the East 

Texas Basin Province, and continues to State waters and 

onshore lands primarily in Louisiana, Mississippi, Arkansas, 

and Alabama in the Louisiana-Mississippi Salt Basins Province. 

The TPS also includes Florida and small parts of Oklahoma, 

Missouri, Illinois, Kentucky, Tennessee, and Georgia (fig. 1). 

The Florida Peninsula Province was not assessed as part of this 

study. The Upper Jurassic-Cretaceous-Tertiary Composite TPS 

contains 33 AUs for undiscovered conventional oil and (or) gas 

resources (table 1) that lie predominantly on the coastal plain 

and in State waters of Texas, Louisiana, Mississippi, Alabama, 

and a small part of the Florida panhandle. The three coalbed 

TPSs contain four AUs (table 1).

Resource Summary

The USGS assessment of undiscovered conventional oil 

and gas resources and continuous coalbed gas resources resulted 

in estimated means of 113.7 trillion cubic feet of gas (TCFG), 

690 million barrels of oil (MMBO), and 3.7 billion barrels of 

natural gas liquids in the AUs that were assessed (table 1). A 

large portion of the undiscovered gas resource is considered to 

be in conventional accumulations trapped in sedimentary strata 

ranging in age from Paleocene to Pliocene-Pleistocene (fig. 2). 

The remaining undiscovered gas resource occurs as continuous coalbed gas in Tertiary and Cretaceous-Tertiary strata. The 

conventional oil and gas resources reside primarily in clastic 

reservoirs deposited on continental shelves, in shelf-margin 

deltas, and in slope fans and basin-floor fans. The continuous 

coalbed gas resources are present within coal beds.

For Additional Information

Supporting geologic studies of Gulf Coast region total 

petroleum systems and assessment units are in progress, as well 

as studies of the methodology used in the assessment of both 

conventional resources in Tertiary strata and continuous coalbed 

gas resources in Cretaceous-Tertiary rocks of the Gulf Coast. 

Assessment results are available at the USGS Central Energy 

Team web site: http://energy.cr.usgs.gov/oilgas/noga

Gulf Coast Assessment Team

Neogene: Russell F. Dubiel (Task Leader, rdubiel@usgs.gov), 

Janet K. Pitman, Ofori N. Pearson

Paleogene: Peter D. Warwick (Task Leader, pwarwick@usgs.gov), 

Alexander W. Karlsen, James L. Coleman, Paul C. Hackley, 

Daniel O. Hayba, Sharon M. Swanson

Review Committee: Ronald R. Charpentier, Troy A. Cook, 

Timothy R. Klett, Richard M. Pollastro, Christopher J. Schenk

Figure 2. Generalized stratigraphic section 

showing geologic units that were assessed 

in the Gulf Coast region. Nomenclature is a 

combination of formal and informal groups, 

and formation and member names that 

are based on physical or biostratigraphic 

correlations in outcrop and subsurface 

studies. The nomenclature reflects the 

common designation and usage in the region 

by State, industry, and academic geologists.

ERATHEM SYSTEM SERIES GEOLOGIC UNIT

Quat. Pleist.

Pliocene Miocene Oligocene Eocene Paleocene

Cenozoic

Tertiary

Vicksburg Group

Jackson Group

Wilcox Group

Midway Group

Upper

Undifferentiated

Undifferentiated

Middle

Lower

Anahuac Formation

Frio

Formation

Hackberry

Upper

Claiborne Group

Lower

Claiborne Group