How are hydrocarbon reserves estimated

There is no universally adopted system according to which hydrocarbon reserves could be classified, but there are some common standards. Russia has recently brought its system closer to them.

Soviet heritage

Hydrocarbon reserves mean the amount of fossil minerals in the Earth’s subsurface, identified during geological exploration and specifically determined at the beginning of production. A classification system was developed in the USSR in 1928. According to this system, reserves were classified as developed proved (category A), explored (category B), and inferred (category C) reserves.


New Russian system

Soviet system of reserves assessment has been improved with time and formed the basis for a new one, which is closer to the international classification standards adopted in 2001. New Russian system suggests the division to the explored reserves (categories A, B, С1), preliminary estimated reserves (category С2), in-place resources (category С3) and forecast resources (category D1, D2). However, Russian standards remain significantly different from the international ones.



In 2007, the Society of Petroleum Engineers (SPE) developed the Petroleum Resources Management System (PRMS). According to the PRMS standards, reserves are classified as proved, probable, and possible. Considered is therefore not only the fact of hydrocarbon discovery in the subsurface, but also the economic efficiency of production. All costs involved in production and transportation, current prices for hydrocarbon feedstock, and other factors are taken into account.

Still stricter – SEC

There are also standards adopted by the US Securities and Exchange Commission (SEC). SEC standards are the strictest, as they set forth most serious requirements for the category of “proved” reserves and consider the period of validity of the license: reserves may not be recognized as proved if their extraction is planned after the expiry of the license.

Global and Russian reserves

Global natural gas reserves including only main production regions, amount to – about 174.14 trillion cubic meters according to international standards. Russia accounts for 47.65 trillion cubic meters, i.e. about one-third of global reserves. Thereby, Gazprom owns about 70 per cent of Russian reserves.

Gazprom reserves are estimated both according to the Russian classification system and PRMS standards. International audit of Gazprom reserves has been conducted by independent engineering companies since 1997. As of December 31, 2010, Gazprom owned 33.1 trillion cubic meters of natural gas; 1.3 billion tons of condensate, and 1.7 billion tons of crude oil according to the Russian reserves classification system. According to international PRMS standards, proved and probable reserves of Gazprom are estimated at 28.7 billion tons of fuel equivalent.