Oil reserves

Oil reserves in the world are judged differently, but is considered to be stocks that can be extracted with the current level of engineering and technology.
National classification
At present, Russia has a system of classification of reserves and resources of oil, gas, condensate, and they contain components that have a commercial value, established by Order of Russian Ministry of February 7, 2001 № 126. According to the degree of scrutiny reserves (resources) into the following categories:
Reserves:
A (explored, studied with full details)
B (explored, studied with detail sufficient for the draft field development)
C1 (explored, studied with detail sufficient to obtain baseline data for the development plan oil or pilot project developing gas fields)
C2 (inferred: the shape and size of the deposit, occurrence, thickness and reservoir properties, composition and properties of the oil, gas and condensate to outline the results of geological and geophysical surveys)
Resources:
C3 (future)
D1l (localized)
D1 (probable reserves of oil and gas litho-stratigraphic complexes, evaluated within large regional structures with proven commercial oil and gas.)
D2 (probable reserves of oil and gas litho-stratigraphic complexes, evaluated within large regional structures, commercial oil and gas not yet proved).

Starting from January 1, 2012 will come into force a new classification, approved by Order of the Ministry of Natural Resources November 1, 2005 № 298. According to this inventory (resources) of oil and gas geological knowledge degree of commercial development will have the following categories:
Reserves:
A (reliable)
B (installed)
C1 (estimated)
C2 (alleged)
Resources:
D1 (localized)
D2 (prospective)
D3 (forecast).
SPE-PRMS classification 
The most common in the world classification, it takes into account not only the probability of finding oil and gas in the field, but also cost-effective production of these reserves. Stock divided into 3 classes
Proved the probability of extracting 90%
Likely-50%
Possible 10% [1]
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UN Classification 
In order to harmonize the national classifications, compilation of best practices, the United Nations in 1990 set about developing a single international classification. The result in 1997 was that the framework of the United Nations Classification for Reserves / Resources: Solid Fuels and Mineral Commodities (UNFC-1997). Currently a framework classification of the United Nations for Fossil Energy and Mineral Reserves and Resources 2009 (UNFC-2009). UNFC-2009 is a universal system in which the number of classified based on three fundamental criteria: the economic and social viability of the project (E), the status and validity of the project to develop the field (F) and the geological knowledge (G), using a numerical coding system. Combination of these three criteria create a three-dimensional system.
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Classifications used in the U.S.
In the U.S., at the same time, there are several classifications of reserves: the classification of the Commission for the Securities Market (SEC), the classification of the Society of Petroleum Engineers (SPE), the classification of the American Association of Petroleum Geologists (AAPG), etc.