DATA SOURCES


     The USGS portion of the National Assessment Project relies largely 
on data that are either published or commercially available. Some USGS
geologic data are from in-progress studies and have not necessarily
been published. In several areas, drilling and production information
was especially sparse or unreliable. Seven major data sources were used
in this assessment:

1. USGS geologic data, both published and unpublished, were used 
   in the development of play definitions, play boundaries, and 
   in the analysis of geologic information concerning undiscovered
   conventional oil and gas accumulations and possible future
   developments in continuous-type oil and gas accumulations.

2. The Significant Oil and Gas Fields of the United States file (NRG)
   is a database commercially available from NRG Associates, Inc.,
   which includes reserves, cumulative production, and various other
   types of information for most oil and gas fields of the United
   States larger than 1 million BOE (NRG Associates, Inc., 1993 and
   1994). The NRG release current as of December 31, 1992 (NRG
   Associates, Inc., 1993), was a major source of reservoir-level
   information for this assessment.

3. The Well History Control System (WHCS) is a commercially available
   database of computerized drilling and completion data from almost
   2.5 million exploratory and development wells available from
   Petroleum Information Corp. (PI). Data were used to construct
   various exploration- and development-intensity maps and plots and
   statistical analyses of drilling and discovery. For most of the
   areas assessed, the 1993 and 1994 versions of WHCS were used
   (Petroleum Information Corp., 1993 and 1994). In most provinces,
   the WHCS contains essentially all wells drilled. However, in
   certain areas, especially the Eastern Region, California, and parts
   of Oklahoma and Louisiana, drilling information is incomplete.

4. Petroleum Information Corp. production data files, including
   monthly, yearly, and cumulative production information from
   numerous recent wells in the United States, were employed to
   construct decline curves and estimated ultimate recovery (EUR)
   distributions used in the analysis of potential additions to
   reserves from continuous-type deposits (Petroleum Information
   Corp., 1994).

5. Energy Information Administration (EIA) Oil and Gas Integrated
   Field File (OGIFF) is a proprietary file of field-level reserves
   and production information. The data in OGIFF are collected
   according to legal mandate by the Department of Energy from
   operators of oil and gas fields of the United States. This file,
   which includes yearly estimates of reserves from fields in the
   United States was used mainly as a database for the prediction of
   potential additions to reserves of known fields. In a few areas of
   sparse data, especially Oklahoma and the Appalachian region, the
   OGIFF was used to supplement NRG for estimation of field sizes.
   Because of the sensitivity of the OGIFF data, however, the output
   provided in this report has been generalized, rounded, or eliminated 
   to avoid releasing any of those data. This is particularly apparent 
   in the output for provinces 055 (Nemaha Uplift), 056 (Forest City 
   Basin), 060 (Cherokee Platform), and 067 (Appalachian Basin).

6. The Energy Information Administration 1993 Annual Report (Energy
   Information Administration, 1994) is the basis of all measured
   (proved) reserve information reported here.

7. Other data, including publications, State records, proprietary
   energy company reports, and other sources, were used by individual
   province geologists. Contributions of time, information, and
   insight by numerous individuals working in the U.S. oil and gas
   industry and State geological surveys were particularly helpful in
   play definition. In certain areas of the country where drilling,
   completion, reserve, or production data are sparse, absent, or
   unreliable, province geologists devoted significant effort to
   compiling original databases for reservoir- and field-level
   information. This was particularly the case for Oklahoma, the
   States of the Appalachian Basin, Louisiana, and California.