1995 National assessment of United States oil and gas resources

The purpose of the National Oil and Gas Resource Assessment Project
is to develop a set of scientifically based hypotheses concerning the
quantities of oil and gas that could be added to the measured (proved)
reserves of the United States.

The word assessment sometimes has the connotation of an inventory.
But this is not the case in this study. The quantities being evaluated here
are largely unknown. This assessment is an attempt to bound the
uncertainties concerning potential additions to oil and gas reserves
under specified conditions. As such, the assessment consists of a set
of constructs, based on the best information and theory available to
the USGS scientists charged with this effort.