Source: Rice University, Jaffe, Medlock, Soligo, accessed 2020-01-08
Figure 2: Simplified representation of the Resource Envelope

Jaffe describes “proved reserves” as subset of resources defined to be economically recoverable. “Economic recoverable” reserves taken as a subset of those accessible technically that in turn are a subset of resources in place (Jaffe, page 16).
Described differently 3-P reserves tend to associate with “technically recoverable resources”. While 2-P reserves are taken as those of provable and probable reserves determined by geology, technology and cost. Where the probable component is that which is not yet identifed but estimated. (Jaffe, page 16)