A Summary of the U.S. Geological Survey 1995 National Assessment of Oil and Gas Resources

"Assuming existing technology, there are approximately 110 billion barrels of technically recoverable oil onshore and beneath State waters; additional resources occur beneath Federal offshore areas. This includes measured (proved) reserves, future additions to reserves in existing fields, and undiscovered resources. The technically recoverable conventional resources of natural gas in measured reserves, future additions to reserves in existing fields, and undiscovered accumulations equal about 715 trillion cubic feet."

Dr. Don Gautier, U.S. Geological Survey

The U.S. Geological Survey (USGS) has completed its portion of the 1995 National Assessment of Oil and Gas Resources.

The purpose of this assessment is to scientifically estimate the amount of oil and gas that could be added to the proved reserves of the United States. The word assessment sometimes connotes an inventory; however, that is not the case in this study. The quantities evaluated here are largely unknown. This assessment attempts to bound the uncertainties concerning potential additions to oil and gas reserves in the onshore areas and beneath State waters. As such, this assessment consists of a set of conclusions based on the best information and theory available to the USGS for those regions. Additional resources reside beneath offshore Federal waters and are being assessed by the Minerals Management Service. The geological assessment of technically recoverable resources makes no attempt to predict at what time or what part of potential additions will be added to reserves. For this National Assessment, resources and potential reserve additions are evaluated regardless of political or economic considerations.



Oil and gas assessment categories for the 1995 assessment are broader in scope than for previous national assessments.

The 1995 assessment considers three categories of resources: undiscovered conventional accumulations of oil and gas; future additions to reserves of known fields (reserve growth or field growth); and, oil and gas in continuous-type accumulations (largely equivalent to "unconventional" categories of other analysts). Each of these three broad categories of resources requires different techniques for evaluation.

Undiscovered conventional accumulations of oil and gas include those postulated to exist outside known fields or accumulations and that, if found, could be recovered using traditional development practices. They exist as discrete accumulations which usually, but not invariably, are defined, controlled, or limited by hydrocarbon/water contacts.

Estimates of national totals for undiscovered technically recoverable conventional oil, gas, and natural gas liquids (NGL) resources; growth of reserves in known fields; technically recoverable resources in continuous-type (unconventional) accumulations; and measured reserves. Gas includes both non-associated and associated-dissolved gas. Fractile values (F₉₅, F₅) are not additive. F₉₅ represents a 19 in 20 chance and F₅ represents a 1 in 20 chance of the occurrence of at least the amount tabulated. NA, not applicable.

Inferred reserves include resources expected to be added to reserves as a consequence of extensions to known fields, through revisions of reserve estimates, and by additions of new pools in discovered fields. Also included in this category are resources expected to be added to reserves through application of improved recovery techniques. Predictions of reserve growth refer to fields found before 1992, the date of most reserve data used for this National Assessment.

For purposes of this assessment, continuous-type accumulations are defined to include those oil and gas resources that exist as geographically extensive accumulations and that generally lack well-defined oil/water or gas/water contacts. This geologically-grounded definition provides a set of consistent criteria to be applied in the determination of whether a specific accumulation is conventional. Such a geological definition intentionally avoids regulatory criteria and does not rely on specific permeability as a defining criterion. Included in this category are coalbed gas, gas in many of the so-called "tight sandstone" reservoirs, and auto-sourced oil- and gas-shale reservoirs. Because of the immense quantities of oil and gas that can be included in this category, only those resources judged to be technically recoverable and that could be added to U.S. oil and gas reserves are reported.



Aggregation of oil and gas resource estimates include geological dependencies between assessment units.

To arrive at the estimated quantity of undiscovered resources for large areas, such as provinces, regions, or the Nation as a whole, distributions estimated for basic assessment units were progressively aggregated with geological dependency incorporated at each level. In order to aggregate plays within provinces, geological dependencies between plays were established for the three basic attributes of charge, reservoir, and trap. Province geologists determined for each pair of plays in their province whether the geological dependence was high, moderate, or low. For aggregation of province-level estimates, the provinces within each region were assigned a moderate dependency. In aggregation of regions for a national total, regions were considered to be geologically independent.



Oil and gas resource estimates are based on a thorough geological and statistical analysis of available data and information.

Within the areas of the USGS assessment, 560 plays were identified, of which about 100 were continuous-type plays and the remaining were conventional plays. Of the 460 conventional plays defined for the 1995 National Assessment, 373 conventional plays were assessed. Of these assessed plays, 290 are confirmed plays and 83 are hypothetical plays. The mean estimate of undiscovered technically recoverable conventional oil resources is slightly more than 30 billion barrels of oil. Of this amount, more than 6 BBO exist in accumulations smaller than 1 million barrels of oil. The mean estimate of undiscovered technically recoverable conventional natural gas is nearly 259 trillion cubic feet. Of this amount, about 45 TCF exist in accumulations smaller than 6 billion cubic feet of gas. The mean estimate of undiscovered natural gas liquids (NGL) is about 7 billion barrels of NGL. It is calculated that reserve growth will add 60 BBO to oil reserves in known fields and 322 TCF will be added to natural gas reserves in known fields during the 80 years following 1991. Technically recoverable hydrocarbon resources from continuous-type accumulations are substantial. The mean estimate for natural gas resources exceeds 300 TCF; the mean estimate for crude oil is about 2 BBO; the mean estimate for natural gas liquids is about 2 BBNGL. For this assessment, the mean estimate of technically recoverable resources of coalbed gas for the lower 48 States is nearly 50 TCF.



The USGS 1995 National Assessment is the most thorough, well-documented, user-friendly assessment of oil and gas resources ever assembled.

The results of the assessment are available on a USGS CD-ROM which is a companion to an executive summary in a USGS Circular. Both products are available through U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225. Though this National Assessment generated very large amounts of data and information, the message is clear. The National Assessment confirms observations that oil production in the United States is in decline as it has been since 1971. But, the future is uncertain. The decline will be less pronounced if, for example, oil prices move higher because this may encourage domestic petroleum exploration. The natural gas situation is different. Production has not yet peaked and the resource is more plentiful. But, this assessment shows that, even to maintain delivery at present levels, industry will need to increase drilling and the Nation will have to address a variety of technological and land-use considerations. As the United States approaches the 21st century, more and more energy is consumed, much of it from fossil fuels. In the United States, a variety of energy sources contributes to meeting needs. Sometimes they compete vigorously. Over the past two decades, citizens have become increasingly aware that use of each source of energy carries with it indirect costs, such as atmospheric change, health risks, damage to land, and vulnerability of supply. Finding solutions to these problems will be a difficult task that requires information that is scientifically-based and non-advocacy in nature. The National Assessment provides just such a view of the oil and gas resources of the United States.

For More Information:

Email: dhouse@usgs.gov