This excerpt taken from the PBR 6-K filed Mar 21, 2006.
(iv) Reserve quantities information
The Companys estimated net proved oil and gas reserves and changes thereto for the years 2005, 2004 and 2003 are shown in the following table. Proved reserves are estimated by the Companys reservoir engineers in accordance with the reserve definitions prescribed by the Securities and Exchange Commission.
Proved oil and gas reserves are the estimated quantities of crude oil, natural gas and natural gas liquids which geological and engineering data demonstrate with reasonable certainty to be recoverable in future years from known reservoirs under existing economic and operating conditions. Proved reserves do not include additional quantities recoverable beyond the term of the concession or contract, or that may result from extensions of currently proved areas, or from application of secondary or tertiary recovery processes not yet tested and determined to be economic.
Proved developed reserves are the quantities expected to be recovered from existing wells with existing equipment and operating methods. Proved undeveloped reserves are those volumes which are expected to be recovered as a result of future investments in drilling, re-equipping existing wells and installing facilities necessary to deliver the production from these reserves.
In some cases, substantial new investments in additional wells and related facilities will be required to recover these proved reserves. Due to the inherent uncertainties and the limited nature of reservoir data, estimates of reserves are subject to change as additional information becomes available.
(iv) Reserve quantities information (Continued)
A summary of the annual changes in the proved reserves of crude oil and natural gas follows: