Definitions, Sources and Explanatory Notes

 Category:   Crude Reserves & Production
 Topic:   Reserves in Nonproducing Reservoirs


Key Terms Definition
Crude Oil A mixture of hydrocarbons that exists in the liquid phase in natural underground reservoirs and remains liquid at atmospheric pressure after passing through surface separating facilities. Crude oil may also include:

  • Small amounts of hydrocarbons that exist in the gaseous phase in natural underground reservoirs but are liquid at atmospheric pressure after being recovered from oil well (casinghead) gas in lease separators, and that subsequently are comingled with the crude stream without being separately measured.
  • Small amounts of nonhydrocarbons produced with the oil.

  • When a State regulatory agency specifies a definition of crude oil which differs from that set forth above, the State definition is to be followed.
    Nonproducing Reserves Quantities of proved liquid or gaseous hydrocarbon reserves that have been identified, but which did not produce during the last calendar year regardless of the availability and/or operation of production, gathering or transportation facilities. This includes both proved undeveloped and proved developed non-producing reserves.
    Proved Reserves of Crude Oil Proved reserves of crude oil as of December 31 of the report year are the estimated quantities of all liquids defined as crude oil, which geological and engineering data demonstrate with reasonable certainty to be recoverable in future years from known reservoirs under existing economic and operating conditions.

    Reservoirs are considered proved if economic producibility is supported by actual production or conclusive formation test (drill stem or wire line), or if economic producibility is supported by core analyses and/or electric or other log interpretations. The area of an oil reservoir considered proved includes: (1) that portion delineated by drilling and defined by gas -- oil and/or gas -- water contacts, if any; and (2) the immediately adjoining portions not yet drilled, but which can be reasonably judged as economically productive on the basis of available geological and engineering data. In the absence of information on fluid contacts, the lowest known structural occurrence of hydrocarbons is considered to be the lower proved limit of the reservoir.

    Volumes of crude oil placed in underground storage are not to be considered proved reserves.

    Reserves of crude oil which can be produced economically through application of improved recovery techniques (such as fluid injection) are included in the "proved" classification when successful testing by a pilot project, or the operation of an installed program in the reservoir, provides support for the engineering analysis on which the project or program was based.

    Estimates of proved crude oil reserves do not include the following: (1) oil that may become available from known reservoirs but is reported separately as "indicated additional reserves"; (2) natural gas liquids (including lease condensate); (3) oil, the recovery of which is subject to reasonable doubt because of uncertainty as to geology, reservoir characteristics, or economic factors; (4) oil that may occur in undrilled prospects; and (5) oil that may be recovered from oil shales, coal, gilsonite, and other such sources. It is necessary that production, gathering or transportation facilities be installed or operative for a reservoir to be considered proved.
    Reservoir A porous and permeable underground formation containing an individual and separate natural accumulation of producible hydrocarbons (oil and/or gas) which is confined by impermeable rock or water barriers and is characterized by a single natural pressure system.

    For definitions of related energy terms, refer to the EIA Energy Glossary.


    "Form EIA-23, "Annual Survey of Domestic Oil and Gas Reserves":  Survey Form

      Explanatory Notes

  • Federal offshore includes Federal offshore Alabama.
  • Miscellaneous includes Arizona, Maryland, Missouri, Nevada, Oregon, South Dakota and Tennessee.
  • Maps of Selected State Subdivisions.