<P> Many countries maintain government - controlled oil reserves for both economic and national security reasons . According to the United States Energy Information Administration, approximately 4.1 billion barrels (650,000,000 m) of oil are held in strategic reserves, of which 1.4 billion is government - controlled . These reserves are generally not counted when computing a nation's oil reserves . </P> <P> A more sophisticated system of evaluating petroleum accumulations was adopted in 2007 by the Society of Petroleum Engineers (SPE), World Petroleum Council (WPC), American Association of Petroleum Geologists (AAPG), and Society of Petroleum Evaluation Engineers (SPEE). It incorporates the 1997 definitions for reserves, but adds categories for contingent resources and prospective resources . </P> <P> Contingent resources are those quantities of petroleum estimated, as of a given date, to be potentially recoverable from known accumulations, but the applied project (s) are not yet considered mature enough for commercial development due to one or more contingencies . Contingent resources may include, for example, projects for which there are no viable markets, or where commercial recovery is dependent on technology under development, or where evaluation of the accumulation is insufficient to clearly assess commerciality . </P> <P> Prospective resources are those quantities of petroleum estimated, as of a given date, to be potentially recoverable from undiscovered accumulations by application of future development projects . Prospective resources have both an associated chance of discovery and a chance of development . </P>

Locale of 10 percent of the worlds oil reserves