Reserves proved/unproved/probable/possible

Petroleum is a resource, in particular, petroleum is a fossil fuel resource (Speight, 1999). A resource is the entire commodity that exists in the sediments and strata whereas the reserves represent that fraction of a commodity that can be recovered economically. However, the use of the term reserves as being descriptive of the resource is subject to much speculation. In fact, it is subject to word variations For example, reserves are classed as proved, unproved, probable, possible, and undiscovered. 

Unproved reserves are based on geologic and/or engineering data similar to that used in estimates of proved reserves but technical, contractual, economic, or rcgulatoiy uncertainties preclude such reseiwes being classified as proved. Unproved reserves may be further divided into two subcategories probable reserves and possible reserves. 

Possible rcsciwcs arc those unproved rcsci vcs which analysis of geological and engineering data suggests are less likely to be recoverable than probable reseiwes. In this context, when probabilistic methods are used, there should be at least a 10 percent probability that the quantities actually recovered will equal or exceed the sum of estimated proved plus probable plus possible reserves. 

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