The terminology used in classifying petroleum substances and the various categories of reserves has been the subject of much study and discussion for many years. The need for an increased degree of standardization has been long recognized but significant difficulty has been encountered in achieving this objective.

A Study Group, comprised of representatives of five member countries of the World Petroleum Congresses (Canada, the Netherlands, the United Kingdom, the United States and Venezuela), reviewed the classification and nomenclature systems for oil and gas and for reserves as used by various countries and recommended systems for universal adoption. Its Interim Report was presented at the 11th Congress held in London In 1983. It has been revised on the basis of comments since that time, and was presented to the 12th Congress held in Houston in 1987.

The recommended systems are scientifically sound, and yet at the same time, practical and simple enough to be readily understood even by those not involved on a daily basis in technical aspects of the industry. The recommended terminology Is as close to current common usage as possible in order to minimize the changes necessary to bring about wide acceptance.

The system recommended by the Group for petroleum reserves refers to Proved Reserves, Unproved Reserves which are categorized as Probable Reserves or Possible Reserves), and Undiscovered Potential Recovery. Further Potential Recovery is the sum of the Proved Reserves, the Unproved Reserves and the Undiscovered Potential Recovery, and the Ultimate Potential Recovery is the sum of the Cumulative Production and the Future Potential Recovery.


The classification of hydrocarbons and the nomenclature of oil and gas reserves have featured in several World Petroleum Congresses (WPC) in one form or another. In 1980, the Executive Board of the UPC decided to set up, for the first time, a Study Group for the 11th Congress in London In 1983, to review

  • the oil and gas classification systems in current use, and focus on the development of a universal system embracing all types of naturally occurring hydrocarbons of present and potential commercial interest, and

  • the nomenclature used by various countries and organizations in reporting estimates of reserves, and focus on the development of a simple, practical, readily understandable system which would receive general acceptance.

This paper deals only with the second item, the nomenclature for reserves.

Canada, the Netherlands, the United Kingdom, the United States of America and Venezuela were invited to nominate one person to the Group, and did so. The individual members are listed at the end of this paper.

National Committees of the WPC were asked for pertinent information about aspects of the Study. The Study Group members exchanged research material and lists of primary definitions and references, and sought opinions from a wide circle of contacts.

The Interim Report was discussed at the llth WPC in London (1983). Additionally, comments were requested from all of the National Committees of the WPC and from certain other organizations.

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