The Oil & Gas Journal (OGJ), a leading source for worldwide reserves estimates that at the end of 2010, worldwide reserves were 1.35 trillion barrels of oil and 6,609 trillion cubic feet or 187 trillion cubic metres of natural gas. These estimates are 14 billion barrels of oil and 348 trillion cubic feet or 10 trillion cubic metres of natural gas higher than the prior year, due to new discoveries.
Discovered (or known) resources can be divided into proved reserves and prospective or unproved (probable and possible) resources. ‘Proved reserves’ are the quantities of oil or gas from known reservoirs and expected to be recoverable with current technology and at current economic conditions. Prospective resources are those that may be recoverable in the future with advanced technologies or under different economic conditions. The application of these distinctions is becoming blurred, For example, in 2003 Canada restated its reserves including its enormous non-conventional oil or tar sands with its conventional oil reserves.
The global energy community is currently engaged in debate about the extent of the world’s remaining oil reserves and the rate of their depletion, and to a lesser extent, gas reserves. Traditional orthodoxy is being challenged and the actual definitions of the resource itself and of the term ‘reserves’ are under scrutiny.
Definitions of oil and gas reserves
Reserves are those quantities of petroleum which are anticipated to be commercially recovered from known accumulations from a given date forward. All reserve estimates involve some degree of uncertainty. The uncertainty depends chiefly on the amount of reliable geologic and engineering data available at the time of the estimate and the interpretation of these data. The relative degree of uncertainty may be conveyed by placing reserves into one of two principal classifications, either proved or unproved. Unproved reserves are less certain to be recovered than proved reserves and may be further sub-classified as probable and possible reserves to denote progressively increasing uncertainty in their recoverability.
