The total in-place resource base of crude oil and natural gas (the amount that existed prior to any production) consists of the total volume that was formed and trapped within the earth’s crust. The in-place resource is a function of the organic content of the source beds from which the hydrocarbons have been derived, the physical conditions under which they formed and migrated, and the effectiveness of the “trap.” (A “trap” is a discontinuity in the properties of the underground formations that, because of reduction in permeability, slows the upward migration of the generated oil and gas so that they accumulate temporarily, although for a long time in human terms, and can be located and produced.) In general, the historically evaluated recoverable portion of the in-place oil and gas resource base is composed of four main parts: cumulative production, proved reserves, indicated and inferred reserves & undiscovered resources