RISKING STRUCTURE


     It is by no means certain that any given play will contain an
undiscovered accumulation. In order to express this uncertainty, a
risking structure was developed based on the three geologic play
attributes of charge, reservoir, and trap.

     Estimates of the probability of occurrence for each of the three
attributes were expressed as decimal fractions between zero and one.
The product of the three values is the play probability (risk = 1 -
probability). Because the three play attributes are not necessarily
independent, care was taken not to apply multiple risks resulting from
a single cause or event.

     In addition to the strictly hypothetical plays, the risking 
structure was also occasionally applied to intensely explored and largely
exhausted plays within which the existence of yet another accumulation
of the minimum size was uncertain. When calculating resources for
hypothetical and largely exhausted plays, the play probability is
applied against the product of the size and number of undiscovered
accumulations estimated to exist in the play. For confirmed plays,
other than those that were nearly exhausted, the play probability was
one. Plays were not quantitatively assessed when the play probability was
0.10 or less.