This paper breaks no new ground in it's call for using practical probabilistic methods for defining reserves. In fact the problem has always begged for a probabilistic solution. The bigger surprise is that an industry which prides itself on its use of science, technology, and frontier risk assessment methodologies finds itself in the 1990's with a reserves definition more reminiscent of the 1890's. The petroleum industry uncovers uncertainty at virtually every stage. Its definitions need to reflect that fact. I hope this paper provides a provocation or two for future debate on this important topic.

When presenting some of these ideas during a panel discussion at the SPE 1991 Annual Technical Meeting, I half jokingly remarked that had the Society been charged with describing the probability of a fair coin, it could not have agreed on a method of quantification:

The Society suggests the following guidelines. Heads: A likely event or an event that certainly may occur. Tails: An entirely possible event or a probable event. Having to attach actual numbers to heads or tails would prove confusing to the membership and will add nothing of value.

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