Proven reserves

"[1] A reserve is considered proven if it is probable that at least 90% of the resource is recoverable by economically profitable means.

Regulatory and contractual conditions may change, and also affect the amount of proven reserves.

Therefore, it is different from the business term which does take into account current break-even profitability, and regulatory and contractual approval, but is considered a very rough equivalent.

However, the purely engineering term is also misleading in that squeezing the last bits of fossil fuel out follows the diminishing returns and at some point is so costly that it becomes highly impractical, as seen on a bell curve, which is why measures like P90 and P95 were created.

[6] Oil companies employ specialist, independent, reserve valuation consultants - such as Gaffney, Cline & Associates, Sproule, Miller and Lents, Ltd., DeGolyer and MacNaughton, Ryder Scott, Netherland, Sewell & Associates Inc. (NSAI), Lloyd's Register (LR Archived 2019-04-15 at the Wayback Machine), Evolution Resources, Cawley, Gillespie & Associates Inc. (CG&A) and others - to provide third party reports as part of Securities and Exchange Commission (SEC) SEC filings and SPE Petroleum Resources Management System (PRMS) for other Stockmarket listings.