Oil reserves are an estimate of the amount of crude oil located in a particular economic region. : Oil reserves are an estimate of the amount of crude oil located in a particular economic region. Oil reserves must have the potential of being extracted under current technological constraints. For example, oil pools situated in unattainable depths would not be considered part of the nation's reserves. Reserves are calculated based on a proven/probably basis. Saudi Arabia, Kuwait, Iran, Iraq, Venezuela, Russia, Mexico, and Canada have some of the world leading oil reserves.