The SPE resource classification system uses “reserves”, “contingent resources” and “prospective resources” to classify hydrocarbon resource of varying technical maturity. The maturity within each class is also described to help guide classification of a given asset.
Annual statement of reserves 2011 (pdf)
Annual statement of reserves 2010 (pdf)
Annual statement of reserves 2009 (pdf)
Annual statement of reserves 2008 (pdf)
Annual statement of reserves 2007 (pdf)