Definitions, Sources and Explanatory Notes

 Category:   Exploration & Reserves
 Topic:   Crude Oil and Natural Gas Exploratory and Development Wells


Key Terms Definition
Crude Oil A mixture of hydrocarbons that exists in liquid phase in natural underground reservoirs and remains liquid at atmospheric pressure after passing through surface separating facilities. Depending upon the characteristics of the crude stream, it may also include:
  • Small amounts of hydrocarbons that exist in gaseous phase in natural underground reservoirs but are liquid at atmospheric pressure after being recovered from oil well (casinghead) gas in lease separators and are subsequently commingled with the crude stream without being separately measured. Lease condensate recovered as a liquid from natural gas wells in lease or field separation facilities and later mixed into the crude stream is also included;
  • Small amounts of nonhydrocarbons produced with the oil, such as sulfur and various metals;
  • Drip gases, and liquid hydrocarbons produced from tar sands, oil sands, gilsonite, and oil shale.

  • Liquids produced at natural gas processing plants are excluded. Crude oil is refined to produce a wide array of petroleum products, including heating oils; gasoline, diesel and jet fuels; lubricants; asphalt; ethane, propane, and butane; and many other products used for their energy or chemical content.
    Development Well A well drilled within the proved area of an oil or gas reservoir to the depth of a stratigraphic horizon known to be productive.
    Dry Hole An exploratory or development well found to be incapable of producing either oil or gas in sufficient quantities to justify completion as an oil or gas well.
    Exploratory Well A hole drilled: a) to find and produce oil or gas in an area previously considered unproductive area; b) to find a new reservoir in a known field, i.e., one previously producing oil and gas from another reservoir, or c) to extend the limit of a known oil or gas reservoir.
    FootageDrilled Total footage for wells in various categories, as reported for any specified period, includes (1) the deepest total depth (length of well bores) of all wells drilled from the surface, (2) the total of all bypassed footage drilled in connection with reported wells, and (3) all new footage drilled for directional sidetrack wells. Footage reported for directional sidetrack wells does not include footage in the common bore that is reported as footage for the original well. In the case of old wells drilled deeper, the reported footage is that which was drilled below the total depth of the old well.
    Natural Gas A gaseous mixture of hydrocarbon compounds, primarily methane, used as a fuel for electricity generation and in a variety of ways in buildings, and as raw material input and fuel for industrial processes.
    Well A hole drilled in the earth for the purpose of (1) finding or producing crude oil or natural gas; or (2) producing services related to the production of crude or natural gas.

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


  • 1949-1965: Gulf Publishing Company, World Oil, "Forecast-Review" issue.
  • 1966-1969: American Petroleum Institute, "Quarterly Review of Drilling Statistics for the United States", annual summaries and monthly reports.
  • 1970-1994: Energy Information Administration (EIA) computations based on well reports submitted to the American Petroleum Institute.
  • 1995 forward: EIA computations based on well reports submitted to the Information Handling Energy Group, Inc.

  •   Explanatory Notes

  • These well counts include only the original drilling of a hole intended to discover or further develop already discovered crude oil or natural gas resources. Other drilling activities, such as drilling an old well deeper, drilling of laterals from the original well, drilling of service and injection wells, and drilling for resources other than crude oil or natural gas are excluded. Due to the methodology used to estimate ultimate well counts from the available partially reported data, the counts shown on this page are frequently revised. More Details from the Monthly Energy Review.
  • For 1949-1959, data represent wells completed in a given year. For 1960-1969, data are for well completion received by the American Petroleum Institute during the reporting year. For 1970 forward, the data represent wells completed in a given year. The as-received well completion data for recent years are incomplete due delays in the reporting of wells drilled. The Energy Information Administration (EIA) therefore statistically imputes the missing data to provide estimates of total well completions and footage where necessary.
  • Geographic coverage is the 50 States and the District of Columbia.