During the 1980’s and 1990’s, new statistical
methods were applied using several risk estimation
techniques such as: (1) lognormal risk resource
distribution (Attanasi and Drew, 1985), (2) Pareto
distribution applied to petroleum field-size data
in a play (Crovelli, 1995) and (3) fractal normal
percentage (Crovelli et al., 1997). Recently, USGS
has developed several mathematical models for
undiscovered petroleum resource assessment (Ahl-brandt and Klett, 2005) and forecast reserve growth
of fields both in the United States (U.S.) and the
world (Klett, 2005)