entral Region Energy Resources Team
U. S. Department of the Interior
Geological Survey


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

Open-File Report 97-463

This report is preliminary and has not been reviewed for conformity with U. S. Geological Survey editorial standards and stratigraphic nomenclature. Any use of trade, product, or company names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.

This Open-File Report is available on CD-ROM
Please contact Energy Team CD Distribution for more information

Field Allocation and Database Compilation: Timothy R. Klett
Province Map Compilation: Lee M. Osmonson
Methodology: James W. Schmoker, Gordon L. Dolton

Province Delineation:


Geologic Provinces
Allocation of Petroleum Resources to Oil and Gas Provinces
Ranking of Provinces


Relative Abundance of Oil versus Gas Fields
Distribution of Petroleum Resources Outside the U. S.
Relationship of Ranking to Reserve Growth
Relationship of Ranking to Undiscovered Resources







This report presents a division of the world into 937 geologic provinces and identifies those that the United States Geological Survey (USGS) plans to assess for petroleum resources. The selection of geologic provinces to be assessed was based on a ranking of known petroleum volumes in terms of barrels of oil equivalent (BOE). Known petroleum volume is defined as cumulative production plus remaining reserves. For the BOE calculation, 6,000 cubic feet of gas equals 1 barrel of oil equivalent.

This ranking of the world's petroleum provinces is a product of the World Energy Project of the USGS, which is undertaking an assessment of the undiscovered oil and gas resources of the world using new assessment methods, new databases, and a total petroleum system approach (Magoon and Dow, 1994). The identification and ranking of geologic provinces comprise the first of a three step assessment process. The second step involves identifying and mapping total petroleum systems within each province. The third step is the assessment of the total petroleum systems. The second and third steps of the assessment process will be described in later reports. Four previous world assessments have been undertaken by the USGS utilizing a Delphi approach and the results were reported by country rather than by geologic province (Masters and others, 1984; 1987; 1991; and 1994).

Those provinces that together represent 95% of the world's known petroleum volume exclusive of the United States (U.S.), are here called priority provinces, and comprise the main group of provinces that will be assessed. Seventy-six provinces were defined as priority provinces. In addition, certain other provinces in the world will be assessed for a variety of political, technical, or geographic reasons and are identified as boutique provinces.

In this report, we define regions and geologic provinces, allocate known petroleum volume of fields to those provinces, and rank the provinces according to the known petroleum volume allocated. We identify priority and boutique provinces for assessment. In addition, we discuss the ranking of provinces and the relation of the ranking to potential reserve growth and undiscovered resources.

METHODS Contents

Regions Contents

The world's land areas are divided here into eight regions (Plate 1) that approximate those used by the U.S. State Department and the U.S. Department of Energy. Each region has been assigned a coordinator and staff responsible for assessment. The regions are (Plate 1): 1, Former Soviet Union; 2, Middle East and North Africa; 3, Asia Pacific; 4, Europe; 5, North America; 6, Central and South America; 7, Sub-Saharan Africa and Antarctica; and 8, South Asia.

Geologic Provinces Contents

We began the assessment by defining geologic provinces of the world (Plate 1, Appendix A2). These encompass all the world's major land areas, and adjoining waters to depths of 2,000 meters. Each geologic province is a spatial entity with common geologic attributes. A province may include a single dominant structural element such as a basin or a fold belt, or a number of contiguous related elements. Province boundaries were drawn as logically as possible along natural geologic boundaries although in some places, for example in the open oceans, they are located arbitrarily.

Provinces were defined by Regional Coordinators and staff from surface and subsurface geologic maps. To aid in defining provinces, digital geologic maps were compiled from the available literature. Provinces of the United States onshore areas and State waters were established in the 1995-1996 U. S. Department of the Interior National Oil and Gas Assessment (Gautier and others, 1995; Minerals Management Service, 1996).

World-wide, 937 geologic provinces (Plate 1, Appendix A) were identified. A four-digit numeric code, in which the first digit represents the region, and a descriptive province name were given to each of the provinces (Appendix A1). Plate 1 shows the province outlines, their assigned numbers, and the regions. Plate 2, in addition to region and province outlines, shows the names and numbers of the priority and boutique provinces as well as the centerpoints of oil and gas fields.

Allocation of Petroleum Resources to Oil and Gas Provinces Contents

About 32,000 fields contained in three oil and gas production databases purchased by the USGS were allocated to world regions and then to geologic provinces. This allocation was based on the location of the field's center point using geographic information systems applications. All subsequent statistics rely on data contained in these databases. Data for United States onshore areas and State waters are from the Significant Oil and Gas Fields of the United States database (NRG Associates, Inc.,1995a) and are current through 1992. Data for U.S. Federal offshore areas are from Minerals Management Service (Lore and others, 1996) and are current through 1994. Canadian data are from the Significant Oil and Gas Pools of Canada database (NRG Associates, Inc., 1995b) and are current through 1993. All other data are from the Petroleum Exploration and Production Database (Petroconsultants, 1996) and are current through the second quarter of 1996. Of the 937 geologic provinces, 406 contain some known petroleum volume. Exclusive of the U. S., 354 provinces contain known petroleum volumes.

Ranking of Provinces Contents

The geologic provinces were ranked by total known petroleum volume in millions of barrels of oil equivalent (MMBOE) within the province. Total known petroleum volume is the sum of the volumes of oil, in barrels; natural gas (combined non-associated gas and associated-dissolved gas), in terms of its energy equivalent in barrels of oil; and natural gas liquids (NGL), in barrels. The ranking, known volumes of commodities, and total known petroleum volume for each petroleum province are shown in Table 1. Figure 1 and Figure 2 show percent cumulative known petroleum volume as a function of province rank for provinces exclusive of the U. S. Figure 3 shows the individual volumes of known petroleum in the 100 top-ranked provinces exclusive of the U. S.

Figure 1Figure 2Figure 3
Figures 1, 2, and 3

Exclusive of the U. S., the 76 largest geologic provinces in terms of petroleum volume contain 95% of the worldís total known petroleum volumes (Table 1). These 76 provinces are the priority provinces that will be assessed. We have database records for more than 14,000 fields located in these priority provinces. In addition to the priority provinces, all boutique provinces will be assessed. Boutique provinces rank below the priority provinces (Table 1). Most of the boutique provinces contain some known volume of petroleum. However, a few currently have no known petroleum volumes documented in the databases used and are listed last in Table 1.

Known petroleum volumes for each of the eight regions are shown in Figure 4. Region 2, Middle East and North Africa, contains the largest known petroleum volume followed by Region 1, Former Soviet Union and by Region 5, North America. The ranking (Table 1) shows that 23 U.S. provinces are among the world's top 100 provinces, placing the large endowment of oil and gas that the U. S. enjoys in a global perspective. The number of geologic provinces in each region that contain known petroleum volumes is also shown in Figure 4. The numbers of priority and boutique provinces in each region are shown in Figure 5.

Figure 4Figure 5
Figures 4 and 5

Priority provinces have been selected based on known petroleum volumes reported in the databases listed earlier, and thus are unlikely to change unless a cutoff other than 95% of the world's total known petroleum volume is adopted. In contrast, boutique provinces were selected on the basis of more subjective factors such as perceived petroleum potential and political relationships. The list of boutique provinces is therefore more subject to additions and deletions in the future.


Field-size distributions by petroleum type for the 76 priority provinces are shown in Appendix B by province number. These field-size distributions provide information about each province regarding: 1) natural endowment of oil and gas volumes; 2) current economic field sizes; 3) relative exploration maturity for oil and gas; and 4) potential for undiscovered resources (missing or under-represented field-size classes).


Relative Abundance of Oil versus Gas Fields Contents

A majority of the world's known petroleum fields are oil fields. Among the priority provinces, the ratio of known oil fields to gas fields is about 2:1, which probably does not reflect the natural endowment of gas relative to oil. In the U.S., where a delivery infrastructure is in place and gas generally finds a ready market, the ratio of oil fields to gas fields is approximately 1:1. In the U.S., the known volume of gas (in BOE) is approximately equal to the known volume of oil. Should technology become available to make gas economically competitive with oil, world gas exploration and development could rapidly become more important.

Distribution of Petroleum Resources Outside the U. S. Contents

Figure 1 and Figure 2 demonstrate the uneven distribution among the petroleum provinces of the world's known petroleum volumes. Exclusive of the U. S., about 80% of the world's known petroleum volume resides in only 7% (24) of the oil and gas provinces; 95% of the world's known petroleum volume resides in 21% (76) of the oil and gas provinces (Table 1). Of the world's almost 20,000 oil and gas fields assigned to provinces in our databases, exclusive of the U. S., 72% (>14,000) reside in the 76 priority provinces.

Relationship of Ranking to Reserve Growth Contents

Initial estimates of the size of newly discovered oil and gas fields commonly are too low. As developmental drilling progresses, successive size estimates of fields usually increase, although some fields deviate from this pattern. The term "reserve growth," which is synonymous with "field growth," refers to this typical increase in the estimated quantity of hydrocarbons in fields that occur as the fields are developed.

In the United States, where petroleum exploration and development are at a more mature stage than the world in general, reserve growth has become the dominant component of future oil and natural-gas resources (U.S. Geological Survey National Oil and Gas Resource Assessment Team, 1995). World-wide, the development of additional oil and natural-gas resources through activities other than new-field exploration (i.e., reserve growth) has become the most important reserve-growth trend of the 1990's (Oil and Gas Journal, 1996, p. 37). Reserve growth is significant now and is likely to become even more important in the future as world demand for oil and gas increases and opportunities for new large-field discoveries decrease. For these reasons, projections of the reserve growth of known fields have become necessary components of petroleum resource assessments.

An assumption implicit in most reserve-growth projections is that reserve growth is proportional to field size-- that is, to known petroleum volume. In the United States, known petroleum volume equates to cumulative production plus proved reserves, and proved reserves are tightly defined. In much of the world, however, known petroleum volume equates to cumulative production plus proved reserves (in the United States sense) plus some component of inferred reserves (which in the United States would be counted as reserve growth). Despite the elusiveness of world-wide reserves reporting, that portion of future reserve growth not already allotted to "proved" reserves can reasonably be assumed to be roughly proportional to known petroleum volume. Thus, the ranking of world oil and gas provinces by known petroleum volume (Table 1) can also be regarded as a ranking according to reserve-growth potential.

Relationship of Ranking to Undiscovered Resources Contents

The world province ranking of Table 1 provides a quantitative rationale for selecting provinces that the USGS will assess for future petroleum resources. As discussed in the previous section, this ranking may also represent the relative reserve-growth potential of the worldís petroleum provinces. For depicting the relative potential for new-field discoveries, however, a ranking scheme would ideally include estimates of undiscovered resources.

However, estimates of undiscovered resources will be the result of the USGS assessment, and are thus unavailable now for a prioritization exercise. An alternative might be to rank world petroleum provinces according to some previous assessment of undiscovered resources. However, geologic-province boundaries used here (Plate 1) do not match the geographic subdivisions of previous world petroleum assessments. For example, the world assessment series by Masters and others (1984; 1987; 1991; 1994) used countries as the basic geographic subdivision.

The world province ranking of Table 1 is based on currently known petroleum volumes -- volumes that have not been adjusted for future reserve growth (which is an assessment result). The possibilities for changes in relative ranking that might be caused by different reserve-growth rates among provinces are mitigated somewhat because many of the worldís large fields were discovered more than two decades ago and have already undergone significant reserve growth.

A possible alternative ranking system would be based on remaining reserves. Such a system would lower the relative ranking of provinces that have large cumulative production. However, the problem of inadequately ranking frontier provinces in which most or all of the petroleum resource is undiscovered would still not be solved. In such frontier provinces, little oil or gas has been produced to date, and known petroleum volume and remaining reserves are essentially equal.

Use of known petroleum volume as the variable for ranking all provinces has at least three advantages for this study: 1) Provinces that have contributed greatly to the worldís energy supply, and have thus been of direct or indirect significance to United States economic security, emerge as high priority; 2) Provinces that have the greatest potential for reserve growth are identified; 3) Mature provinces where undiscovered resources are close to well developed infrastructure, and where marginal costs will be low, tend to be ranked relatively high.

The petroleum endowment of geologic provinces has a highly skewed distribution (for example, Figure 1 and Figure 2), so that a rich province in which only a relatively small share of the conventional petroleum endowment remains undiscovered can still rank high on a world scale of undiscovered petroleum potential. Stated overly simply, our ranking of provinces according to known petroleum volume embodies this idea that "acorns are found near oak trees". Our boutique-province designations focus attention on those frontier areas where the existence of a substantial petroleum endowment is suspected but not yet established in the form of known petroleum volume. Some boutique provinces include regionally extensive, so-called unconventional or continuous-type hydrocarbon resources that may become viable in the 30-year time frame of this assessment.

SUMMARY Contents

This report provides a ranking of the world's geologic provinces according to known petroleum volume. Exclusive of the U.S., about 80% of the world's known petroleum volume resides in 7% (24) and 95% in 21% (76) of the oil and gas provinces. The ranking facilitates studies of reserve growth, assessment of undiscovered resources, and analysis of economics and risk. The ranking also provides a balanced perspective of U.S. petroleum provinces with respect to the rest of the world.


Gautier, D. L., Dolton, G. L., Takahashi, K. I., and Varnes, K. L., 1995, 1995 National
     Assessment of United States Oil and Gas Resources - Results, Methodology, and
     Supporting Data: U.S. Geological Survey Digital Data Series DDS-30.

Lore, G. L., Brooke, J. P., Cooke, D. W., Klazynski, R. J., Olson, D. L., and Ross, K. M.,
     1996, Summary of the 1995 assessment of conventionally recoverable hydrocarbon
     resources of the Gulf of Mexico and Atlantic Outer Continental Shelf: Minerals
     Management Service OCS Report MMS 96-0047, 67 p.

Magoon, L. B., and Dow, W. G., eds., 1994, The petroleum system - from source to trap:
     American Association of Petroleum Geologists Memoir 60, 655 p.

Masters, C. D., Root, D. H., and Dietzman, W. D., 1984, Distribution and quantitative
     assessment of world crude oil reserves and resources: Proceedings of 11th World
     Petroleum Congress, v. 2, p. 229-237.

Masters, C. D., Attanasi, E. D., Dietzman, W. D., Meyer, R. F., Mitchell, R. W., and Root, D.
     H., 1987, World resources of crude oil, natural gas, natural bitumen, and shale oil:
     Proceedings of 12th World Petroleum Congress, v. 5, p. 3-27.

Masters, C. D., Root, D. H., and Attanasi, E. D., 1991, World resources of crude oil and natural
     gas: Proceedings of 13th World Petroleum Congress, v. 2, p. 51-64.

Masters, C. D., Root, D. H., and Attanasi, E. D., 1994, World petroleum assessment and
     analysis: Proceedings of 14th World Petroleum Congress, p. 529-541.

Minerals Management Service, 1996, An assessment of the undiscovered hydrocarbon potential of
     the Nation's Outer Continental Shelf: Minerals Management Service OCS Report MMS
     96-0034, 40 p.

NRG Associates, Inc., 1995a [includes data current as of December 31, 1992], The significant oil
     and gas fields of the United States database: Colorado Springs, Colo., NRG Associates,
     Inc., [database available from NRG Associates, Inc., P.O. Box 1655, Colorado Springs,
     CO 80901].

NRG Associates, Inc., 1995b [includes data current as of December 31, 1993], The significant oil
     and gas fields of Canada database: Colorado Springs, Colo., NRG Associates, Inc.,
     [database available from NRG Associates, Inc., P.O. Box 1655, Colorado Springs, CO

Oil and Gas Journal, 1996, Oil and gas reserves, oil output rise in 1996: Oil and Gas Journal, v.
     94 (December), n. 53, p. 37-38.

Petroconsultants, 1996, Petroleum exploration and production database: Houston, Texas,
     Petroconsultants, Inc., [database available from Petroconsultants, Inc., P.O. Box 740619,
     Houston, TX 77274-0619].

U.S. Geological Survey National Oil and Gas Resource Assessment Team, 1995, 1995 National
     Assessment of United States Oil and Gas Resources: U.S. Geological Survey Circular
     1118, 20 p.

Top of Report TOP of Report BACK to World Energy Publications Back to World Energy logo  Take Pride in America button