INTRODUCTION


     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.

     The U.S. Geological Survey has occasionally conducted assessments of
the oil and gas resources of the United States since shortly after the
turn of the century. Each successive assessment is a refinement of
previous work. Systematic National Assessments have been conducted more
regularly since 1975. In 1982, the Minerals Management Service was
formed and given responsibility for resource evaluation in the Federal
offshore areas of the United States. The USGS retained responsibility
for onshore areas and State waters. In 1991, the two organizations
(USGS and MMS) began their second joint study of the oil and gas
resources of the United States. This report summarizes the results of
the USGS part of that study and reports estimates of potential
additions to reserves onshore and under State waters of the United
States.  Documentation for this assessment is available on the CD-ROM that
supports this report (Gautier and others, 1995).

     The previous USGS/MMS assessment (Mast and others, 1989) encompassed
estimates of both technically recoverable and economically recoverable
resources. The present report concerns only technically recoverable
resources. A parallel study concerns the economic evaluation of the
resources described in this report. The geological assessment of
technically recoverable resources makes no attempt to predict at what
time or what part of potential additions will be added to reserves. For
the National Assessment, resources and potential reserve additions are
evaluated regardless of political, economic, and other considerations.

     The onshore and State water areas of the United States were divided
into eight regions consisting of 71 provinces (fig. 3). These regions
and provinces are similar, but not identical, to those addressed by
U.S. Geological Survey Circular 860 (Dolton and others, 1981) and the
U.S. Department of the Interior report from the previous National
Assessment of oil and gas resources(Mast and others, 1989). Within
these provinces, about 560 plays were assessed, of which about 100 were
in continuous-type deposits; the remainder were hypothetical and
confirmed conventional plays.

     The estimates presented in this document reflect USGS understanding 
as of January 1, 1994, and are intended to capture the range of
uncertainty, to provide indicators of the relative potential of various
petroleum provinces, and to provide a guide useful in considering
possible effects of future oil- and gas-related activities within the
United States.