National and Global Petroleum Assessment

Assessment of Undiscovered Continuous Oil and Gas Resources in 

the Monterey Formation, Los Angeles Basin Province, California, 2015

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2016–3036

July 2016 Printed on recycled paper

Oil AU. Conventionally trapped oil and gas 

fields with oil-water contacts were excluded 

from the areas of the AUs. Assessment 

unit boundaries outline the areas in which 

generation of oil began as the base of the 

organic-rich Monterey Formation rocks 

reached burial depths of about 9,000 

to 12,000 ft. The Central and Eastern 

Los Angeles Monterey Continuous Oil

AU is defined by the -12,000-foot structure contour near the base of the Monterey 

Formation, from the map of Wright (1991, 

fig. 10). The Western Shelf Los Angeles 

Monterey Continuous Oil AU includes 

the area west of the Newport-Inglewood 

fault zone where the base of the Monterey 

Formation is deeper than 9,000 feet, 

interpolated from Wright’s (1991) map. 

Geochemical evidence suggests that the top 

of this zone may be about 12,000 ft deep 

in the eastern part of the basin but is likely 

to be somewhat shallower, about 9,000 ft 

deep, west of the Newport-Inglewood fault 

zone where the organic matter in the rocks 

contains more sulfur, allowing it to generate 

oil with less heating.

Figure 1. Map of the Los Angeles Basin Province in California with boundaries of the two 

assessments defined in this study.

Introduction

The U.S. Geological Survey (USGS) 

completed a geology-based assessment of 

technically recoverable continuous petroleum resources in the Miocene Monterey 

Formation in the Los Angeles Basin 

Province of southern California (fig. 1). Continuous petroleum accumulations are those 

in which oil or gas is pervasively present in 

essentially all wells that penetrate them, that 

may not be structurally or stratigraphically 

trapped, and that typically lack oil-water 

or gas-water contacts. They are commonly 

produced with well-stimulation technology, 

such as hydraulic fracturing, that is commonly referred to as “unconventional.” The 

same stimulation technology, however, is 

also used in many conventionally trapped 

accumulations. The Monterey Formation is 

the source rock for the oil that accumulated 

in conventional structural and stratigraphic 

traps in the Los Angeles Basin, including 

the giant Wilmington and Huntington Beach 

oil fields.

Previous studies of the Los Angeles 

Basin assessed a mean of 0.98 billion 

barrels of undiscovered oil (Beyer, 1996) 

and a mean of 3.2 billion barrels of potential 

additions to reserves in discovered oil fields 

(Gautier and others, 2012). This assessment 

addresses potential resources in a continuous accumulation of oil in the Monterey 

Formation at depth, in or near the zone of 

petroleum generation, where petroleum that 

has not migrated to shallower conventional 

traps could still be present.

Definition of Assessment Units

Two assessment units (AUs) were 

defined for these rocks: (1) the Central 

and Eastern Los Angeles Monterey 

Continuous Oil AU and (2) the Western 

Shelf Los Angeles Monterey Continuous

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

13 million barrels of oil, 22 billion cubic feet of gas, and 1 million barrels of natural gas liquids in the Monterey Formation of the 

Los Angeles Basin Province, California.

–119° –118°

34°

Source: National Park Service

PACIFIC

OCEAN

Central and

Eastern Los Angeles

Monterey Continuous Oil AU 

Western Shelf

Los Angeles Monterey

Continuous Oil AU

Los Angeles

Basin Province

!

Los Angeles

C A L I F O R N I A

Los Angeles Basin Province

Western Shelf Los Angeles Monterey Continuous Oil AU

Central and Eastern Los Angeles Monterey Continuous 

 Oil AU

EXPLANATION

County boundary

Area

of study

PACIFIC

OCEAN

CA

NV

0 15 30 KILOMETERS

0 15 30 MILES
Using the southern San Joaquin Basin, 

where the Monterey Formation reflects a 

similar depositional setting, as an analog for 

estimating success rates, well productivity, 

and spacing, we concluded that although 

some recoverable oil may remain in the 

source rock, success rates (proportion of 

drilled wells that produce at least 2,000 barrels) will be low, and the estimated ultimate 

recoveries will be small even for successful 

wells (table 1). Wells would be relatively 

tightly spaced, as they are in productive 

Monterey Formation reservoirs in conventional traps in the San Joaquin Basin to 

the north.

Undiscovered Resource Summary

The USGS assessed undiscovered, 

technically recoverable continuous oil 

and gas resources in two AUs in the 

Monterey Formation of the Los Angeles 

Basin Province (table 2). Estimated mean 

resources are 8 MMBO, 15 billion cubic 

feet of gas (BCFG), and 1 million barrels 

of natural gas liquids (MMBNGL) in the 

Central and Eastern Los Angeles Monterey 

Continuous Oil AU and 5 MMBO, 

7 BCFG, and 0 MMBNGL in the Western 

Shelf Los Angeles Monterey Continuous 

Oil AU. The estimated volumes of potential 

recoverable oil in deep Monterey Formation 

continuous accumulations are small compared to those in possible undiscovered conventional accumulations or from potential 

additional recovery from producing fields. 

Anticipated extraction methods are mostly 

Assessment input data Central and Eastern Los Angeles Monterey Continuous Oil AU

Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 40,000 110,000 220,000 123,667

Average drainage area of wells (acres) 5 10 40 18.3

Success ratio (%) 5 10 40 18.3

Average EUR (MMBO) 0.003 0.005 0.02 0.006

AU probability 1.0

Assessment input data Western Shelf Los Angeles Monterey Continuous Oil AU

Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 20,000 55,000 127,000 67,333

Average drainage area of wells (acres) 5 10 40 18.3

Success ratio (%) 5 10 50 21.6

Average EUR (MMBO) 0.003 0.005 0.02 0.006

AU probability 1.0

Table 1. Key assessment input data for the two continuous assessment units in the 

Los Angeles Basin Province, California.

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

average EUR input is the minimum, median, maximum, and calculated mean. Shading indicates not applicable]

Total petroleum system and

assessment units (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

Monterey Total Petroleum System

Central and Eastern Los Angeles 

Monterey Continuous Oil AU 1.0 Oil 2 6 19 8 3 11 37 15 0 0 2 1

Western Shelf Los Angeles

Monterey Continuous Oil AU 1.0 Oil 1 4 13 5 2 5 18 7 0 0 1 0

Total undiscovered continuous

resources 3 10 32 13 5 16 55 22 0 0 3 1

Table 2. Assessment results for two continuous assessment units in the Los Angeles Basin Province, California.

[AU, assessment unit; 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. 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]

vertical (rather than horizontal) wells and 

acid stimulation; hydraulic fracturing is less 

likely to be successful.

References Cited 

Beyer, L.A., 1996, Los Angeles Basin 

Province (014), in Gautier, D.L., Dolton, 

G.L., Takahashi, K.I., and Varnes, K.L., 

1996, 1995 National Assessment of 

United States oil and gas resources—

Results, methodology, and supporting 

data: U.S. Geological Survey Data Series 

DDS–30, release 2, 1 CD-ROM. [Also 

available at http://certmapper.cr.usgs.gov/

data/noga95/prov14/text/prov14.pdf.]

Gautier, D.L., Tennyson, M.E., Cook, 

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

2012, Remaining recoverable petroleum 

in ten giant oil fields of the Los Angeles 

Basin, southern California: U.S. Geological Survey Fact Sheet 2012–3120, 

v. 1.1, 2 p.

Wright, T.L., 1991, Structural geology and tectonic evolution of the 

Los Angeles Basin, California, chap. 3,

part 1, of Biddle, K.T., ed., Active 

margin basins: American Association 

of Petroleum Geologists Memoir 52, 

p. 35–134.

Los Angeles Basin Monterey Assessment Team

Marilyn E. Tennyson, Ronald R. Charpentier, Timothy R. Klett, Michael E. Brownfield, Janet K. Pitman, Stephanie B. 

Gaswirth, Sarah J. Hawkins, Phuong A. Le, Paul G. Lillis, Kristen R. Marra, Tracey J. Mercier, Heidi M. Leathers-Miller, and 

Christopher J. Schenk

For More Information

Assessment results are available at the USGS Energy Resources Program Web site at http://energy.usgs.gov.

ISSN 2327-6916 (print) ISSN 2327-6932 (online) http://dx.doi.org/10.3133/fs20163036