Exploration experience in the local area is entered here.
This serves to use bayesian methods to update the world-wide prior
probability of hydrocarbon charge to be updated to a local prior P[HC].
In addition the P[O | HC] , the conditional probability of having liquid oil, given that HC are discovered. is estimated and the P[C | FG], the conditional probability to have condesate in the free gas. Here a cutoff richness of two barrels per million cubic feet is used, to distinguish wet from dry gas.
The numbers resulting from the counting are used to update the world-wide beta parameters, the parameters r' and n' . This results in more, or less favourable parameters of a posterior beta distribution, r" and n". The latter "local" parameters become in turn prior parameters in the next update procedure, which involves the local petroleum system data, resulting in the final P[HC], etc. for the prospect.
It will be clear that the above bayesian approach is fundamentally different from a direct subjective assessment of the chances of fulfillment in a PSA.