Classifications

Reserves are those quantities of petroleum claimed to be commercially recoverable by application of development projects to known accumulations under defined conditions.[6] Reserves must satisfy four criteria: They must be:
discovered through one or more exploratory wells[6]
recoverable using existing technology[6]
commercially viable[6]
remaining in the ground[6]
All reserve estimates involve uncertainty, depending on the amount of reliable geologic and engineering data available and the interpretation of those data. The relative degree of uncertainty can be expressed by dividing reserves into two principal classifications - proved and unproved.[6] Unproved reserves can further be divided into two subcategories - probable and possible to indicate the relative degree of uncertainty about their existence.[6] The most commonly accepted definitions of these are based on those approved by the Society of Petroleum Engineers (SPE) and the World Petroleum Council (WPC) in 1997