For anyone interested there is a link to some  quick reading, in...

For anyone interested there is a link to some  quick reading, in a summary style of a very smart guy on this topic - Dr. Pete Rose, he is basically the guru of explaining Pg or Geological chance of success and its evolution over the last 30 yrs.

Pg 

Five Factors:

- Hydrocarbon Source Rocks

- Migration and Timing

- Reservoir Rocks

- Closure (Structural or Strati-graphic)

- Containment (Seal, Preservation)

When multiplied, represent the chance of an active HC- system yielding oil/gas in quantities enough to sustainflow;

ie, P99 RESERVES OR MORE: The Chance of Landing on the Prospect Resources Distribution.

http://www.searchanddiscovery.com/pdfz/documents/2017/42063rose/ndx_rose.pdf.html