Depletion Rate: the amount of crude oil currently being extracted as a percentage of the amount yet-to-extract. Simple formula: (Amount extracted) / (Amount yet-to-extract).

Amount extracted / Produced-to-date: total amount of crude oil that has been extracted from proved reserves as of a given date.

Yet-to-extract / Yet-to-produce: (Discovered oil — Produced oil) + Undiscovered oil. Simple formula: (Reserves) + (Yet-to-find).

Reserves: quantities of crude oil and gas (both discovered and undiscovered) anticipated to be economically recoverable from discovered / proved sources. Oil in the ground is not a reserve unless is it estimated to be economically recoverable. Simple formula: (Discovered oil) — (Produced oil).

Discovered Reserves / Proved Reserves: reserves that can be estimated with a high degree of certainty to be recoverable using current technology at current prices. Reserves do not include oil that has been produced / extracted.

Undiscovered Reserves / Yet-to-find Reserves: quantities of crude oil estimated on a given date to be potentially recoverable from discovered accumulations, but which are not currently economic to extract.

Discovered & Undiscovered Unrecoverable Resources: unrecoverable resources, whether discovered or not, are neither technically possible nor economic to produce.

Prospective Resources: quantities of oil and gas estimated on a given date to be potentially recoverable from undiscovered accumulations.