National Assessment of Oil and Gas Fact Sheet

Assessment of Undiscovered Oil and Gas Resources of 

the San Joaquin Basin Province of California, 2003

Introduction

The U.S. Geological Survey (USGS) recently 

completed an assessment of the undiscovered oil and 

gas potential of the San Joaquin Basin Province of 

California (fig. 1). The assessment is based on the 

geologic elements of each total petroleum system 

defined in the province, including hydrocarbon 

source rocks (source-rock type and maturation, and 

hydrocarbon generation and migration), reservoir 

rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and 

timing). Using this geologic framework, the USGS 

defined 5 total petroleum systems and 10 assessment 

units within these systems. Undiscovered oil and gas 

resources were quantitatively estimated for the 10 

assessment units (table 1).

Resource Summary

With respect to undiscovered conventional 

hydrocarbon resources in the San Joaquin Basin 

Province, the USGS estimated means of 1.7 trillion

cubic feet of gas (TCFG), 393 million barrels of oil (MMBO), and 86 

million barrels of total natural gas liquids (MMBNGL) for the five total 

petroleum systems (exclusive of reserve growth in existing oil and gas 

fields). Well over half of both the mean undiscovered gas resource 

(62 percent, 1 TCFG) and the mean NGL resource (67 percent, or 57 

MMBNGL) is in the Deep Fractured Pre-Monterey Assessment Unit 

of the Eocene-Miocene Composite Total Petroleum System (table 1). 

Of the mean 393 MMB of total undiscovered oil, about 328 MMBO 

(83 percent) is estimated to be in five assessment units of the Miocene 

Total Petroleum System, and 46 MMBO (12 percent) is estimated for 

the Eocene West Side Fold Belt Assessment Unit of the Eocene Composite Total Petroleum System (table 1). Nearly 31 percent, or 121 

MMB, of the total mean undiscovered oil resource in the San Joaquin 

Basin Province is estimated to be in the Central Basin Monterey Diagenetic Traps Assessment Unit.

Using a geology-based assessment 

methodology, the U.S. Geological 

Survey estimated a mean of 1.7 trillion 

cubic feet of undiscovered natural gas, 

a mean of 393 million barrels of 

undiscovered oil, and a mean of 86 

million barrels of natural gas liquids in 

the San Joaquin Basin Province.

Potential reserve growth in existing oil and gas fields in the 

San Joaquin Basin Province was calculated during our study. 

Based on the analyses of recovery efficiencies and remaining oilin-place, we estimated that another 3.5 billion barrels of oil may 

be added to reserves in existing fields. Most additional reserves 

may come from improved recovery in diatomite reservoirs of the 

Miocene Monterey Formation. This estimate of potential reserve 

growth suggests that most oil in the future may come from existing fields rather than from new oil field discoveries in the San 

Joaquin Basin.

Figure 1. San Joaquin Basin Province of California.

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS-2004-3043

April 2004 Printed on recycled paper

Printed on recycled paper
For Further Information

Supporting geologic studies of total petroleum systems, assessment units, reserve growth, and the methodology used in the San Joaquin 

Basin Province assessment are in progress. Assessment results are available at the USGS Central Energy Team website,

http://energy.cr.usgs.gov/oilgas/noga.

San Joaquin Basin Province Assessment Team

Donald L. Gautier (Task Leader; gautier@usgs.gov), Allegra Hosford Scheirer, Marilyn E. Tennyson, Kenneth E. Peters, Leslie B. 

Magoon, Paul G. Lillis, Ronald R. Charpentier, Troy A. Cook, Christopher D. French, Timothy R. Klett, Richard M. Pollastro, and 

Christopher J. Schenk.

Table 1. San Joaquin Basin Province assessment results.

[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 fields, all liquids are 

included under the NGL (natural gas liquids) category. F95 denotes a 95 percent chance of at least the amount tabulated. Other fractiles are defined similarly. Fractiles are additive, assuming perfect positive correlation. TPS, Total Petroleum System; AU, Assessment Unit. Gray shading indicates not applicable]

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