Disregarding economics, the proper "engineering" term for the total technologically extractable amount is the Producible fraction, which is easily confused with the "business" term "proven reserves". 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. The term "proven reserves" is further subdivided into "proved developed reserves" and "proved undeveloped reserves". Note that it does not include "unproven reserves", which is broken down into "probable reserves" as well as "possible reserves".