U.S. Gulf Coast Petroleum Systems Project

Assessment of Undiscovered Continuous Oil and Gas Resources in the 

Upper Cretaceous Tuscaloosa Marine Shale of the U.S. Gulf Coast, 2018

Introduction

The U.S. Geological Survey (USGS) completed a geology-based 

assessment of undiscovered, technically recoverable oil and gas resources 

in the continuous, self-sourced reservoir in the Upper Cretaceous Tuscaloosa marine shale of Louisiana, Mississippi, Alabama, and Florida in the 

U.S. Gulf Coast region (fig. 1). The assessed interval is part of the Upper 

Jurassic–Cretaceous–Tertiary Composite Total Petroleum System (TPS) 

in onshore lands and State waters of the U.S. Gulf Coast region. The 

Tuscaloosa marine shale is an organic-rich, siliceous mudstone of the late 

Cenomanian to Turonian. Its thickness is as much as 495 feet (ft), and the 

vertical depths of the reservoirs in currently producing horizontal wells 

are from 11,000 to 14,000 ft.

Geologic Model for Assessment

The Upper Cretaceous Tuscaloosa Marine Shale Continuous Oil 

Assessment Unit (AU) is in central Louisiana, southern Mississippi, 

southern Alabama, and Florida State waters. Its boundaries are defined 

primarily by thermal maturity, where measured and modeled values 

from 0.6 to 1.3 percent vitrinite reflectance (Ro

) indicate that Upper 

Cretaceous strata are mature for oil generation over a broad area on the 

paleoshelf and for wet gas and condensate generation on the paleoslope 

area. The AU boundary in offshore Louisiana, Mississippi, Alabama, 

and Florida follows the State-Federal water boundary.

For the northern boundary, thermal maturity of 0.6 percent Ro

 is 

reached at about 9,000-ft subsurface in the Upper Cretaceous regionally, 

with certain exceptions. Using a gridded surface for depth to the base 

of the Tuscaloosa marine shale (top of lower Tuscaloosa Formation), 

the 9,000-ft structural contour generally defined the northern extent 

of the Tuscaloosa Marine Shale Continuous Oil AU. The northern AU 

boundary was placed at depths less than 9,000 ft in areas where measured thermal maturity of 0.6 percent Ro

 is reached at shallower depths. 

Thermal maturity models in east Texas (J. Pitman, USGS retired, unpub. 

data, 2017) and Louisiana (Pitman and Rowan, 2012) provided guidance 

in western Louisiana where there is limited measured data. In southeastern Mississippi, the northern boundary was placed at depths less than 

9,000 ft to account for multiple measured percent Ro

 values (including 

measurements of solid bitumen reflectance) from the Cretaceous, which 

show that the Upper Cretaceous section is in the oil-generative window 

(greater than 0.6 percent Ro

). Further, the heat-flow map by Blackwell 

and others (2011) showed that southern Mississippi is an area of relatively higher heat flow compared to southern Louisiana and Alabama. 

The southern boundary of the Tuscaloosa Marine Shale Continuous Oil AU was delineated where measured and modeled values indicate 

the thermal maturity of the Tuscaloosa marine shale is less than or 

equal to 1.3 percent Ro

. The southern boundary of the AU was placed at 

the 19,000-ft subsurface contour from near Pine Prairie, La., eastward 

through central Louisiana and was based on measured vitrinite reflectance 

values from shales in the Tuscaloosa marine shale and in the upper part 

of the Tuscaloosa Formation. In the Mississippi Bird’s Foot delta area 

(St. Bernard, Balize, and Plaquemine lobes), low thermal maturity is 

from recent river avulsion and deposition of a thick package of cold 

sediment (Rittenour and others, 2007). Low thermal maturity was confirmed by measured percentage of Ro

 values in Tuscaloosa marine shale 

samples from a well drilled approximately 14 miles east of Hopedale, 

La., and petrographic and geochemical analysis indicated a thermally 

immature, undifferentiated Cretaceous section in a well in Mississippi 

Canyon Block 84 by Wagner and others (1994). These results influenced 

the divergence of the southern boundary from the 19,000-ft contour in 

southeastern Louisiana. At the southern margin of the AU in western 

Louisiana, thermal maturity rises to about 1.3 percent Ro

 at about 

15,000-ft subsurface as interpolated from burial history modeling projected eastward from Texas (Pitman and Rowan, 2012; J. Pitman, USGS 

retired, unpub. data, 2017). The southeastern AU boundary follows 

the State-Federal water boundary in offshore Louisiana, Mississippi, 

Alabama, and Florida.

Subsurface mapping in the Sabine Uplift indicates Cenomanian 

sediments were not deposited. Placement of the northwestern boundary 

of the Tuscaloosa Marine Shale Continuous Oil AU near Clare, La., near 

the Louisiana-Texas State line was influenced by stratigraphic thinning of 

Figure 1. Map showing the Tuscaloosa Marine Shale Continuous 

Oil Assessment Unit (AU) and related portions of the U.S. Geological 

Survey-defined Louisiana-Mississippi Salt Basins Province and 

Western Gulf Province (Klett and others, 1997).

WESTERN GULF

LOUISIANA-MISSISSIPPI SALT BASINS

LOUISIANA

TEXAS MISSISSIPPI

ALABAMA

ARKANSAS

FLORIDA

GULF OF MEXICO

Clare

Pine Prairie

Hopedale

28°

30°

32°

–94° –92° –90° –88°

Base map from U.S. Department of the Interior 

National Park Service

0 50 100 MILES

0 100 KILOMETERS 50

TX

AL

LA MS

OK AR GA

FL

TN

Map area

GULF OF MEXICO

EXPLANATION

Province boundary and identifier

Louisiana-Mississippi Salt Basins Province

Western Gulf Province 

Tuscaloosa Marine Shale Continuous Oil AU

WESTERN

GULF

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2018–3043

August 2018

Using a geology-based assessment methodology, the U.S. Geological Survey assessed mean undiscovered, technically recoverable continuous 

resources of 1.5 billion barrels of oil and 4.6 trillion cubic feet of gas in the Upper Cretaceous Tuscaloosa marine shale in onshore and State waters of 

Louisiana, Mississippi, Alabama, and Florida in the U.S. Gulf Coast region.
Table 1. Key input data for one assessment unit (AU) in the Tuscaloosa marine shale of Louisiana, 

Mississippi, Alabama, and Florida in the U.S. Gulf Coast region. 

[AU, assessment unit; %, percent; EUR, estimated ultimate recovery per well; MMBO, million barrels of oil. Well 

drainage area, success ratio, and EUR are defined partly using U.S. shale-oil analogs. The average EUR input is 

the minimum, median, maximum, and calculated mean. Shading indicates not applicable]

Assessment input data

Tuscaloosa Marine Shale Continuous Oil AU

Minimum Mode Maximum Calculated 

mean

Potential production area of AU (acres) 1,500 1,500,000 20,411,000 7,304,167

Average drainage area of wells (acres) 75 150 185 136.7

Untested area (%) 90 94 99 94.3

Success ratio (%) 5 25 75 35.0

Average EUR (MMBO) 0.04 0.08 0.2 0.086

AU probability 1.0

Table 2. Results for one continuous assessment unit (AU) in the Tuscaloosa marine shale of Louisiana, Mississippi, Alabama, and Florida in the U.S. Gulf Coast region. 

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

accumulations, all liquids are included in the NGL category. 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. Shading indicates not applicable]

Total petroleum system 

and assessment unit (AU)

AU

probability

Accumulation 

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 Total Petroleum System

Tuscaloosa Marine Shale 

Continuous Oil AU 1.0 Oil 181 1,151 4,215 1,537 529 3,406 12,742 4,614 15 99 393 138

Total undiscovered 

continuous resources 181 1,151 4,215 1,537 529 3,406 12,742 4,614 15 99 393 138

the Upper Cretaceous section from east and west onto the 

structural high of the Sabine Uplift as projected downdip. 

The western boundary of the AU follows the LouisianaTexas State line where the stratigraphic nomenclature 

changes; the Tuscaloosa Formation is recognized east of 

this boundary, whereas to the west, correlative strata are 

included in the Eagle Ford Group (Adams and Carr, 2010). 

Self-sourced hydrocarbons in the Cenomanian–

Turonian shale of the Tuscaloosa Marine Shale Continuous 

Oil AU include black and volatile oils (35–48 American 

Petroleum Institute [API] gravity) in the shallower, 

paleoshelf areas where vitrinite reflectance is less than 

1.1 percent Ro and wet gas and condensate (greater than 

45 API gravity) in the deeper paleoslope areas where vitrinite reflectance is 1.1 percent Ro

 to about 1.3 percent Ro.

Banner image of thin-section photographs of the Tuscaloosa marine shale from 

Pike County, Mississippi, shows alginite and forams in reflected light (front) and 

blue-light excitation (back). Photographs by Celeste D. Lohr, U.S. Geological Survey.

Undiscovered Resources Summary

The USGS assessed undiscovered, technically recoverable 

continuous resources in Louisiana, Mississippi, Alabama, and Florida 

State waters of the U.S. Gulf Coast region (table 2). Assessed mean 

resources for the Tuscaloosa Marine Shale Continuous Oil AU are 

1,537 million barrels of oil (MMBO), or 1.5 billion barrels of oil; 

4,614 billion cubic feet of gas (BCFG), or 4.6 trillion cubic feet of 

gas; and 138 million barrels of natural gas liquids (MMBNGL). 

For the Tuscaloosa Marine Shale Continuous Oil AU, the assessed 

oil resources have an F95–F5 range from 181 to 4,215 MMBO, 

the assessed gas resources have an F95–F5 range from 529 to 

12,742 BCFG, and the assessed natural gas liquids resources have 

an F95–F5 range from 15 to 393 MMBNGL.

References Cited

Adams, R.L., and Carr, J.P., 2010, Regional depositional systems of the 

Woodbine, Eagle Ford, and Tuscaloosa of the U.S. Gulf Coast: Gulf 

Coast Association of Geological Societies Transactions, v. 60, p. 3–27. 

Blackwell, D., Richards, M., Frone, Z., Batir, J., Ruzo, A., Dingwall, R., and 

Williams, M., 2011, Temperature-at-depth maps for the conterminous 

U.S. and geothermal resource estimates, in Geothermal Resources 

Council Annual Meeting 2011, San Diego, Calif., October 23–26, 2011: 

Geothermal Resources Council Transactions, v. 35, p. 1545–1550.

Klett, T.R., Ahlbrandt, T.S., Schmoker, J.W., and Dolton, G.L., 1997, 

Ranking of the world’s oil and gas provinces by known petroleum 

volumes: U.S. Geological Survey Open-File Report 97–463, 1 

CD–ROM, accessed January 18, 2018, at https://pubs.usgs.gov/of/1997/

ofr-97-463/97463.html.

Pitman, J.K., and Rowan, E., 2012, Temperature and petroleum generation 

history of the Wilcox Formation, Louisiana: U.S. Geological Survey 

Open-File Report 2012–1046, 51 p., accessed September 1, 2017, at 

https://pubs.usgs.gov/of/2012/1046.

Rittenour, T.M., Blum, M.D., and Goble, R.J., 2007, Fluvial evolution of 

the lower Mississippi River valley during the last 100-kyr glacial cycle—

Response to glaciation and sea-level change: Geological Society of 

America Bulletin, v. 119, p. 586–608.

Wagner, B.E., Sofer, Z., and Claxton, B.L., 1994, Source rock in the 

Lower Tertiary and Cretaceous deep-water Gulf of Mexico: Gulf Coast 

Association of Geological Societies Transactions, v. 44, p. 729–736.

Tuscaloosa Marine Shale Assessment Team

Paul C. Hackley, Catherine B. Enomoto, Brett J. Valentine, William A. Rouse, Celeste D. Lohr, Frank T. Dulong, Javin J. Hatcherian, 

Sean T. Brennan, William H. Craddock, Thomas M. Finn, Stephanie B. Gaswirth, Phuong A. Le, Heidi M. Leathers-Miller, Kristen R. Marra, 

Tracey J. Mercier, Stanley T. Paxton, Katherine J. Whidden, Cheryl A. Woodall, and Christopher J. Schenk

For More Information

Assessment results are also available at the USGS Energy Resources Program website at https://energy.usgs.gov.

ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20183043