The occurrence and quantity of world petroleum resources appears to be well understood. The numbers are so great, however, that even minor variants in the total picture can be responsible for enormous localized industrial activity. Specific knowledge of the widespread local occurrences of oil and gas, therefore, is important to economic development and to the free market distribution of energy. It is also clear, however, that a large proportion of the recoverable petroleum resources are found in only a few selected localities. We believe that, worldwide, recoverable conventional oil and gas exist in ultimate quantities approximating 2300 billion barrels (370 Gm3) of oil and 12 000 trillion cubic feet (340 TM3) of gas. These values are limited by our concepts of world petroleum geology and our understanding of specific basins; nonetheless, continued expansion of exploration activity, around the world, has resulted in only minimal adjustments to our quantitative understanding of ultimate resources. Reserves reporting has been one of the greatest hindrances to a thorough understanding of world resources because we are just now gaining an understanding of field growth and what is actually being calculated and reported from various localities. Unconventional resources are present in large quantities, in particular in the Western Hemisphere, and are of a dimension to substantially contribute to world reserves should economic conditions permit.

The following publications were prepared in the course of World Energy Studies by program scientists. Most are open-file reports because we consider it our prime responsibility to get the program supporting data into the public record. Various of the authors have also seen fit to publish their work in refereed scientific journals and those publication outlets are also listed.The summation of the program work is reported in the proceedings volumes of the World Petroleum Congresses-see Global section of the bibliography. In those reports, petroleum resource data were aggregated by major petroleum resource countries. It is our intention to ultimately report resource data by petroleum basin in order to provide a closer tie of resource understanding and petroleum geology.

The estimates of undiscovered conventionally recoverable petroleum resources in the northwest European region at probability levels of 95 percent, 5 percent, statistical mean, and mode are for oil (in billions of barrels): 9, 34, 20, and 15; and for gas (in trillions of cubic feet): 92, 258, 167, and 162. The occurrence of petroleum can be accounted for in two distinct geological plays located in the various subbasins of the region. Play I is associated with the distribution of mature source rocks of Late Jurassic age relative to four distinct trapping conditions. The play has been demonstrated productive mostly in the Viking and Central Grabens of the North Sea, where the shale has been buried to optimum depths for the generation of both oil and gas. To the north of 62 ? N. latitude up to the Barents Sea, source rocks become increasingly deeply buried and are interpreted to be dominantly gas prone; a narrow band of potentially oil-prone shales tracks most of the coast of Norway, but water depths in favorable localities commonly range from 600 to 1,200 feet. To the south of the Central Graben, the Jurassic source rocks are either immature or minimally productive because of a change in facies. Undrilled traps remain within the favorable source-rock area, and exploration will continue to challenge the boundaries of conventional wisdom, especially on the Norwegian side where little has .been reported on the geology of the adjoining Bergen High or Horda Basin, though, reportedly, the Jurassic source rocks are missing on the high and are immature in the southern part of the basin. Play II is associated with the distribution of a coal facies of Carboniferous age that is mature for the generation of gas and locally underlies favorable reservoir and sealing rocks. The play is limited largely by facies development to the present area of discovery and production but is limited as well to the southeast into onshore Netherlands and Germany by the unfavorable economics of an increasing nitrogen content in the gas. This increase is apparently caused by excessive temperatures associated with increasing depth of burial of the source rock. The history of discovery in the North Sea would appear to deny the commonly held maxim that large fields are found first and early in the exploration process. However, if the discovery data are examined from the perspective of the award date of each exploration license, then it is clear that the largest fields and most of the reserves have indeed been found early in the exploration process of a particular license. Discoveries made within 1 year of granting the license are on average large giants, and they account for slightly less than two-thirds of the original reserves. Discoveries made within 2 to 5 years of the granting of the license are on average less than giant size and smaller than increment-l-year discoveries by a factor of 4; these fields account for a little less than one-third of the reserves. Those fields found 6 or more years after the granting of the license are relatively small and account for 20 percent of all discoveries but only 4 percent of total original reserves. These data suggest that a measure of an area's exploration maturity is the length of time elapsed since the award of the concession.

World Demonstrated Reserves of crude oil are approximately 723 billion barrels of oil (BBO). Cumulative production is 445 BBO and annual production is 20 BBO. Demonstrated Reserves of crude-oil have declined over the past 10 years consistent with discoveries lagging production over the same period. The assessment of Undiscovered Resources shows a 90 percent probability that the amount discoverable lies between 321 and 1,417 BBO, 550 BBO being the most likely value. The most likely value for Ultimate recoverable resources is 1,718 BBO. The distribution of Ultimate Resources of crude oil will remain highly skewed toward the Middle East; no frontier areas that have potentials large enough to significantly affect present distribution are recognized. Rates of discovery have continued to decline over the past 20 years even though exploration activity has increased in recent years. Prudence dictates, therefore, that the low side of the assessment of Undiscovered Resources be responsibly considered and that alternate energy sources be a part of future planning. Extra-heavy oil and bitumen are assessed separately, with Reserves being figured as the annual productive capacity of installed facilities times 25 years. The annual production of extra-heavy oil is about 8 million barrels and of bitumen about 60 million barrels.

S. Geological Survey (USGS).The program is designed to prepare geologically based resource assessments of the potential petroleum basins of the world.Initial investigations of the program focus on the major petroleum-producing regions of the world with the objective of acquiring a critical

The following preliminary report is a product of the World Energy Resources Program of the U.S. Geological Survey (USGS).The program is designed to prepare geologically based resource assessments of the potential petroleum basins of the world.Initial investigations of the program focus on the major petroleum-producing regions of the world with the objective of acquiring a critical

The following preliminary report is a product of the World Energy Resources Program of the U.S. Geological Survey (USGS).The program is designed to prepare geologically based resource assessments of the potential petroleum basins of the world.Initial investigations of the program focus on the major petroleum-producing regions of the world with the objective of acquiring a critical

National resource assessments are intended to give some insight into future possibilities for the recovery of a desired resource. The resource numbers themselves only useful when related to economically controlled factors, such as industry capability as reflected in rated of production, rates of discovery, and technology development. To that end, it is useful to divide the resource base into component parts to which appropriate econometrics can be applied. A system of resource reporting adhering to these principles has been agreed to by the two major resource agencies in Government, the U>S. Geological Survey and the U.S. Bureau of Mines (USGS Bulletin 1450-A). Conceptually, then, a plan for resource reporting has been devised, and all resource reporting by these two agencies follows the agreed-upon pattern. Though conceptual agreement has been reached, each commodity has its own peculiar data problems; hence an operational definition to fit the conceptual pattern must be evolved for each mineral. Coal is the only commodity to date for which an operational agreement has been reached (USGS Bulletin 1450-B), but the basic essentials of an operational classification within the guideline of Bulletin 1450-A have been reported for oil and gas in USGS circular 725. The basic classification system is now well established and received general endorsement by Resources for the Future in a study of mineral resource classification systems prepared for the the Electric Power Research Institute (Schanz, 1976), and with respect to coal by the International Energy Agency.