In February of 1987 the Society of Petroleum Engineers, SPE, approved its ‘Definitions for Oil and Gas Reserves' and, during the same year, the 'Classification and Nomenclature Systems for Petroleum and Petroleum Reserves’ of the World Petroleum Congress (WPC) was approved at the 12th WPC. Both, the SPE and WPC's Reserves Definitions were the result of extensive research throughout all sectors of the Oil Industry in most of the oil producing countries.

Even though there was no coordination or discussion between the two groups responsible for these efforts, the concepts and definitions in the two documents are very similar. Since then discussions have continued to be held throughout the world, with the participation of different sectors of the Oil Industry, on some of the concepts included in the SPE Definitions.

Venezuela has actively participated in both of these efforts and continues to contribute with permanent representatives in the working groups. Internally these concepts have been used extensively when estimating Venezuelan reserves and in the revisions that took place in 1987, it justified the addition of approximately 25 o00 MMB to the country's proved oil reserves.

This paper discusses the concepts included in these documents and attempts to evaluate the relative merits of the arguments for and against the Definitions. Also discussed, as an example of the utility of these definitions, is the use that Venezuela has made of these concepts.


Oil and gas reserve definitions have always been a controversial subject. The origin of such controversy is multiple. On one side most engineers and geologists have been involved in reserves estimation and assessment, for short or long periods, at any one time of their careers. Thus, most of them, by now managers, company or government officers have some personal experience with the subject and usually hold strong opinions on the matter.

Furthermore, hydrocarbon reserves are a very important asset for countries and corporations the world over. Therefore, there is the natural tendency to accept or reject the definitions that are perceived as beneficial or detrimental to a particular position.

A standard set of definitions is even more important when it is considered that the greatest majority of the known oil and gas resources of the world are Stateowned, and government regulations set the standards and procedures for reserves estimations. Moreover, reserve figures are not only the product of technical and economical calculations; strategic and political values are implicitly assigned to these figures. At times all factors together make the def

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