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Energy Glossary

Energy Glossary & Acronym List


Energy Glossary

bitumen - A generic term applied to natural inflammable substances of variable color, hardness, and volatility, composed principally of a mixture of hydrocarbons substantially free from oxygenated bodies.

A - B - C - D - E - F - G - H - I - J -K - L - M - N - O - P - Q - R - S - U,V,W,X,Y,Z


accumulation - A pool of petroleum locally confined by subsurface geologic features.

acid mine drainage - Often referred to as AMD, refers to the outflow of acidic water from (usually abandoned) metal mines or coal mines. 

anthracite - The highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of fixed carbon and a low percentage of volatile matter.

API gravity - American Petroleum Institute (API) gravity is a measure of how heavy or light a petroleum liquid is compared to water. If its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks. It is used to compare the relative densities of petroleum liquids.

aquifer - An aquifer is a formation, group of formations, or part of a formation that contains sufficient saturated permeable material to yield significant quantities of water to wells and springs.

assessment unit - An assessment unit is a volume of rock within the Total Petroleum System that encompasses fields, discovered and undiscovered, sufficiently homogeneous in terms of geology, exploration strategy and risk characteristics to constitute a single population of field characteristics with respect to criteria used for resource assessment.



barrels of oil equivalent (BoE) - A unit of petroleum vol­ume in which the gas part is expressed in terms of its energy equivalent in barrels of oil. 

bitumen - A generic term applied to natural inflammable substances of variable color, hardness, and volatility, composed principally of a mixture of hydrocarbons substantially free from oxygenated bodies.

bituminous coal - Middle rank coal (between subbituminous and anthracite) formed by additional pressure and heat on lignite. Usually has a high Btu value and may be referred to as "soft coal."

breccia pipe - A breccia pipe is a mass of breccia (a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix) often in an irregular and cylindrical shape. They usually consist of fragments of the host rock (the rock layer they are contained in) cemented together by silica. These formations are often hosts for ore deposition especially in copper and uranium mining districts.

Btu (British thermal unit) - The amount of heat needed to raise the temperature of 1 pound of water by 1 degree fahrenheit. The Btu is a convenient measure by which to compare the energy content of various fuels.

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Cambrian - A Period in the geologic time scale that spans from approximately 570 to 505 million years ago.

carbon - Symbol C--A naturally abundant nonmetallic element that occurs in many inorganic and in all organic compounds, exists freely as graphite and diamond and as a constituent of coal, limestone, and petroleum, and is capable of chemical self-bonding to form an enormous number of chemically, biologically, and commercially important molecules.

carbon dioxide (CO2) - A colorless, odorless, incombustible gas, present in the atmosphere and formed during respiration, usually obtained from coal, coke, or natural gas by combustion, from carbohydrates by fermentation, by reaction of acid with limestone or other carbonates, or naturally from springs.

carbon sequestration - Both natural and deliberate processes by which CO2 is either removed from the atmosphere or diverted from emission sources and stored in the ocean, ter­restrial environments (vegetation, soils, and sediment), and geologic formations. 

cleat - The vertical cleavage of coal seams. The main set of joints along which coal breaks when mined.

coal - A readily combustible black or brownish-black rock whose composition, including inherent moisture, consists of more than 50 percent by weight and more than 70 percent by volume of carbonaceous material. It is formed from plant remains that have been compacted, hardened, chemically altered, and metamorphosed by heat and pressure over geologic time.

coal basin - A region in which coal deposits of known or possible economic value occur within a basinal structure.

coal quality - The character or nature of the amount of impurities (ash and trace elements) in coal. Coal quality parameters of greatest interest include ash, moisture, sulfur, and energy value (also known as heat content).

coalbed gas - See "coalbed methane."

coalbed methane (CBM) - Coalbed methane is a form of natural gas generated by and extracted from coal beds. In recent decades it has become an important source of energy in the United States and other countries.

coke (coal) - A solid carbonaceous residue derived from low-ash, low-sulfur bituminous coal from which the volatile constituents are driven off by baking in an oven at temperatures as high as 2,000 degrees Fahrenheit so that the fixed carbon and residual ash are fused together. Coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. Coke from coal is grey, hard, and porous and has a heating value of 24.8 million Btu per short ton.

coke (petroleum) - A residue high in carbon content and low in hydrogen that is the final product of thermal decomposition in the condensation process in cracking. This product is reported as marketable coke or catalyst coke. The conversion is 5 barrels (of 42 U.S. gallons each) per short ton. Coke from petroleum has a heating value of 6.024 million Btu per barrel.

continuous oil & gas accumulations - Commonly are regional in extent, have diffuse boundaries, and are not buoyant on a column of water. Continuous accumulations have very low matrix permeabilities, do not have obvious seals and traps, are in close proximity to source rocks, are abnormally pressured, and have relatively low recovery factors. Included in the category of continuous accumulations are hydrocarbons that occur in tight sand reservoirs, shale reservoirs, basin-centered reservoirs, fractured reservoirs, and coal beds.

continuous oil accumulation - A "continuous” or "unconventional" oil accumulation means that the oil resource is dispersed throughout a geologic formation rather than existing as discrete, localized occurrences, such as those in conventional accumulations. Unconventional resources often require special technical drilling and recovery methods.

conventional oil & gas accumulations - Are discrete accumulations with well-defined hydrocarbon-water contacts, where the hydrocarbons are buoyant on a column of water. Conventional accumulations commonly have relatively high matrix permeabilities, have obvious seals and traps, and have relatively high recovery factors.

crude oil - A mixture of liquid hydrocarbons that exists in natural underground reservoirs as distinguished from refined oils manufactured from it. Does not include liquid hydrocarbons produced from tar sand, gilsonite, oil shale, or coal.

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deposit - Mineral deposit or ore deposit is used to designate a natural occurrence of a useful mineral, or an ore, in sufficient extent and degree of concentration to invite exploitation.

discovered - Hydrocarbons whose location and quantity are known or estimated from specific geologic evidence are discovered resources. Discovered resources include known resources, unproved reserves, and proved reserves depending upon economic, technical, contractual, or regulatory criteria.

drainage - The manner in which the water of an area passes or flows off by surface streams or subsurface conduits.

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economically recoverable resources - Are that part of the assessed technically recoverable resource for which the costs of finding, development, and production, including a return to capital, can be recovered by production revenues at a given price.

enhanced oil recovery - Injection of steam, gas, or other chemical compounds into hydrocarbon reservoirs to stimulate the production of usable oil beyond what is possible through natural pressure, water injection, and pumping at the wellhead. 

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F05 - 5th fractile--represents a 5 percent chance of at least the amount tabulated.

F50 - 50th fractile--represents a 50 percent chance of at least the amount tabulated.

F95 - 95th fractile--represents a 95 percent chance of at least the amount tabulated.

federally owned offshore areas - Federal jurisdiction begins at 3 geographic (nautical) miles from the established baseline for the coast and extends to an outer limit of 200 nautical miles. However, there are special cases. Because of claims existing at the dates of statehood, Texas and the Gulf Coast of Florida have proprietary interest in a submerged belt of land, 9 geographic miles wide, extending seaward along the coast. Resource assessments in federally owned offshore areas are typically done by the Bureau of Ocean Energy Management (BOEM). 

field - An accumulation, pool, or group of pools of hydrocarbons or other mineral resources in the subsurface. A hydrocarbon field consists of a reservoir with trapped hydrocarbons covered by an impermeable sealing rock, or trapped by hydrostatic pressure.

formation - A body of rock strata, of intermediate rank in the hierarchy of lithostratigraphic units, which is unified with respect to adjacent strata by consisting dominantly of a certain lithologic type, or by possessing other unifying lithologic features.

fossil - Any remains, trace, or imprint of a plant or animal that has been preserved in the Earth's crust since some past geologic or prehistoric time. Fossils are found in sedimentary rocks.

fossil fuel - A general term for any hydrocarbon that may be used for fuel: chiefly oil, natural gas, and coal.

fracking - See "hydraulic fracturing"

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gas - Also referred to as natural gas, is a naturally occurring hydrocarbon gas mixture consisting primarily of methane with up to 20 percent of other hydrocarbons as well as impurities in varying amounts.

gas hydrates - Naturally occurring “ice-like” combinations of natural gas and water that have the potential to provide an immense resource of natural gas from the world’s oceans and polar regions. Gas hydrates are known to be widespread in permafrost regions and beneath the sea in sediments of outer continental margins. It is generally accepted that the volume of natural gas contained in the world's gas hydrate accumulations greatly exceeds that of known gas reserves.

gas:oil ratio (GOR) - Ratio of gas to oil (in cubic feet per barrel) in a hydrocarbon accumulation. GOR is calculated by using volumes of gas and oil at surface conditions. 

gas reservoir - A subsurface accumulation of hydrocarbons primarily in the gas phase that is contained in porous or fractured rock formations. A gas accumulation is defined by the USGS as having a gas:oil ratio of 20,000 cubic feet per barrel or greater. 

geologic carbon sequestration (CO2) - A method of securing carbon dioxide in deep geologic formations to prevent its release to the atmosphere and contribution to global change as a greenhouse gas.

geology - The study of the planet Earth---the materials of which it is made, the processes that act on these materials, the products formed, and the history of the planet and its life forms since its origin.

geothermal - Pertaining to the heat of the interior of the Earth.

global warming - An increase in the average temperature of the Earth's surface, atmosphere, and oceans which occurs following an increase in greenhouse gases.

greenhouse effect - A complex natural process that takes place when gases in the Earth's atmosphere, including water vapor, allow heat energy from the Sun to pass through to the land and oceans. Heat energy radiating from the Earth's surface is absorbed by atmospheric gases, known as greenhouse gases, and is re-radiated back to Earth instead of escaping into space. This natural process may be affected by human activities, such as emitting large quantities of carbon dioxide into the atmosphere.

greenhouse gases - Gases that absorb heat re-radiated from the surface of the Earth. The greenhouse gases are carbon dioxide, chlorofluorocarbons (CFCs), methane, nitrous oxide, ozone, and water vapor.

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heavy oil - Heavy oil is any type of crude oil which does not flow easily. It is referred to as "heavy" because its density or specific gravity is higher than that of light crude oil. Heavy oil has been defined as any liquid petroleum with an API gravity less than 20 degrees.

hydrate - A compound formed by the union of water with some other substance.

hydraulic fracturing - Also referred to as hydrofracking, hydrofracturing, and fracking, is a well development process that involves injecting water under high pressure into a bedrock formation via the well. This is intended to increase the size and extent of existing bedrock fractures.

hydrocarbon - Any organic compound, gaseous, liquid, or solid, consisting solely of carbon and hydrogen.

hydrofracking - See "hydraulic fracturing"

hydrofracturing - See "hydraulic fracturing

hydrostatic pressure - The pressure which is exerted on a portion of a column of water as a result of the weight of the fluid above it.

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in-place resources - In-Place resources are those quantities of petroleum that are estimated, as of a given date, to be contained in known accumulations prior to production. The quantity which can be commercially produced or mined, may be significantly less than the volumes estimated to be in place.

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 joule - joule the standard unit of energy in electronics and general scientific applications. One joule is defined as the amount of energy exerted when a force of one newton is applied over a displacement of one meter. One joule is the equivalent of one watt of power radiated or dissipated for one second. One British thermal unit (Btu) is equivalent to approximately 1055 joules.

kerosene - A colorless flammable oil distilled from petroleum. Used for fuel for jet engines, heating, cooking, and lighting.

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light crude - Liquid petroleum that has a low density and flows freely at room temperature. It has a low viscosity, low specific gravity, and high API gravity due to the presence of a high proportion of light hydrocarbon fractions.

liptinite - a brownish-black coal that is intermediate in coalification between peat and subbituminous coal with a calorific value less than 8300 BTU/pound on a moist, mineral-matter-free basis. 

lithology - The description of rocks, especially in hand specimen and in outcrop, on the basis of characteristics such as color, mineralogic composition, and grain size. 

lithostratigraphic unit - A body of rock that is unified by consisting dominantly of a certain lithologic type or combination of types, or possessing other unifying lithologic features.

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maceral - an organic substance in coal that is distinguished and classified (see maceral classification) on the basis of its optical microscopic properties.

manganese - An element designated by the symbol Mn and atomic number 25. It is found as a free element in nature (often in combination with iron), and in many minerals. Manganese is a metal with important industrial metal alloy uses, particularly in stainless steel.

marginal resources - An oil or gas resource for which the economics of the field are barely able to cover the costs of production.

mean - The arithmetic average.

mercury - Mercury is an element with the symbol Hg and atomic number 80. A heavy, silvery element, mercury is the only metal that is liquid at standard temperature and pressure. Mercury is often associated with coal deposits.

methane - A colorless, odorless gas, the simplest parafin hydrocarbon, formula CH4. It is the principal constituent of natural gas and is also found associated with crude oil. Methane is a greenhouse gas in the atmosphere because it absorbs long-wavelength radiation from the Earth's surface. 

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nahcolite resources - Nahcolite is a soft carbonate mineral with the composition of sodium bicarbonate (NaHCO3). Among other occurrences, nahcolite resources are present in the oil shale deposits of the Parachute Creek Member of the Eocene Green River Formation. It occurs as disseminated aggregates, nodules, bedded units of disseminated brown crystals, and white crystalline beds associated with dawsonite (NaAl(OH)2CO3) and halite (NaCl).

natural gas - See also "gas." Hydrocarbons that exist as a gas or vapor at ordinary pressure and temperature. Methane is the most important, but ethane, propane, and others may be present. Common impurities include nitrogen, carbon dioxide, and hydrogen sulfide. Natural gas may occur alone or associated with oil.

natural gas basin - A depressed area in the Earth's crust, of tectonic origin, in which sediments have accumulated and natural gas has been generated and/or accumulated, and/or migrated.

natural gas field - A region or area that possesses or is characterized by natural gas.

natural gas liquids - Those hydrocarbons in natural gas that are separated from the gas as liquids through the process of absorption, condensation, adsorption, or other methods in gas processing or cycling plants. Natural gas liquids include natural gas plant liquids (primarily ethane, propane, butane, and isobutane) and lease condensate (primarily pentanes produced from natural gas at lease separators and field facilities).

natural gas play - The active exploration or leasing of land for natural gas.

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oil - A naturally occurring complex liquid hydrocarbon, which after distillation and removal of impurities yields a range of combustible fuels, petrochemicals, and lubricants. Crude oil refers to oil as it emerges from a well but before refining or distillation.

oil & gas basin - A region in which oil and gas of known or possible economic value occurs within a basinal structure.

oil reservoir - A subsurface accumulation of hydrocarbons composed primarily of oil that is contained in porous or frac­tured rock formations. An oil accumulation is defined by the USGS as having a gas:oil ratio less than 20,000 cubic feet per barrel. 

oil sands - Are a combination of clay, sand, water, and bitumen, a heavy black viscous oil. Oil sands can be mined and processed to extract the oil-rich bitumen, which is then refined into oil. The bitumen in oil sands cannot be pumped from the ground in its natural state; instead oil sand deposits are mined, usually using strip mining or open pit techniques, or the oil is extracted by underground heating with additional upgrading.

oil shale - A kerogen-bearing, finely laminated brown or black sedimentary rock that will yield liquid or gaseous hydrocarbons on distillation. Oil shale, despite the name, does not actually contain oil, but rather a type of organic matter called kerogen, a precursor of oil that is converted to a type of crude oil when heated to about 450 – 500° C.

organic petrology - That branch of geology dealing with the origin, occurrence, structure, and history of organic matter, especially coal. 

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permeability - A measure of the ability of a rock to permit fluids to be transmitted through it; it is controlled by pore size, pore throat geometry, and pore connectivity. Permeability is typically reported in darcies. 

porosity - The part of a rock that is occupied by voids or pores. Pores can be connected by passages called pore throats, which allow for fluid flow, or pores can be isolated and inaccessible to fluid flow. 

petroleum - A general term for all naturally-occurring hydrocarbons, whether gaseous, liquid, or solid.

produced waters - Produced water is a term used to describe water that is produced along with oil and gas.

proved reserves - Those quantities of petroleum which, by analysis of geological and engineering data, can be estimated with reasonable certainty to be commercially recoverable, from a given date forward, from known reservoirs and under current economic conditions, operating methods, and government regulations.

province - A geologic or geomorphic province is a spatial entity with common geologic or geomorphic attributes. A province may include a single dominant structural element such as a basin or a fold belt or a number of contiguous related elements.

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recoverability - In reference to accessible coal resources, the condition of being physically, technologically, and economically minable. Recovery rates and recovery factors may be determined or estimated for coal resources without certain knowledge of their economic minability; therefore, the availability of recovery rates or factors does not predict recoverability. A measure of mining or extraction efficiency.

reserve growth - Reserve growth is the increase in estimated volumes of oil and natural gas that can be recovered from existing fields and reservoirs through time. Most reserve growth results from delineation of new reservoirs, field extensions, or improved recovery techniques thereby improving efficiency, and recalculation of reserves due to changing economic and operating conditions.

reserves - are those quantities of petroleum anticipated to be commercially recoverable by application of
development projects to known accumulations from a given date forward under defined conditions. Reserves must further satisfy four criteria: they must be discovered, recoverable, commercial, and remaining (as of the evaluation date) based on the development project(s) applied.

reserves, possible - Those unproved reserves which analysis of geological and engineering data suggests are less likely to be recoverable than probable reserves (probability 10-50%) (SPE).

reserves, probable - Those unproved reserves which analysis of geological and engineering data suggests are more likely than not (>50% probability) to be recoverable (SPE).

reserves, proved - Those quantities of petroleum which, by analysis of geological and engineering data, can be estimated with reasonable certainty (90% probability) to be commercially recoverable, from a given date forward, from known reservoirs and under current economic conditions, operating methods, and government regulations (SPE).

reservoir - A subsurface, porous, permeable rock body in which oil or gas or both have accumulated.

resinite - a liptinite maceral occurring as rounded, ovoid, or rod-like bodies assuming the shape of an enclosing cell lumen or as irregular shapes filling cracks in the coal.

resources - are those quantities of petroleum (both conventional and unconventional) occurring naturally within the earth's crust and include both discovered and undiscovered accumulations.

resource assessment - The process by which one estimates the location, amounts, and production of a resource. The USGS assesses undiscovered, technically recoverable resources.


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sample (coal) - A representative fraction of a coal bed collected by approved methods, guarded against contamination or adulteration, and analyzed to determine the nature; chemical, mineralogic, and (or) petrographic composition; percentage or parts-per-million content of specified constituents; heat value; and possibly the reactivity of the coal or its constituents.

seal - A geologic feature that inhibits the mixing or migration of fluids and gases between adjacent geologic units. A seal is typically a rock unit or a fault; it can be a top seal, inhibiting upward flow of buoyant fluids, or a lateral seal, inhibiting the lateral flow of buoyant fluids.

seal formation - The confining rock unit within the carbon dioxide storage assessment unit. The seal formation is a rock unit that suf­ficiently overlies the storage formation and where managed properly has a capillary entrance pressure low enough to effec­tively inhibit the upward buoyant flow of liquids or gases. 

sedimentary basin - A sedimentary basin refers to any geological feature exhibiting subsidence and consequent infilling by sediments.

selenium - A chemical element with the symbol Se and atomic number 34.

shale gas - Shale gas refers to natural gas that can be generated and trapped within shale units.

shale oil - Shale oil refers to liquid petroleum that can be generated and trapped within shale units.

source rock - Rocks containing relatively large amounts of organic matter that is transformed into hydrocarbons.

state waters - State jurisdiction begins at the established baseline for the coast and extends 3 geographic (nautical) miles. However, there are special cases. Because of claims existing at the dates of statehood, Texas and the Gulf Coast of Florida have proprietary interest in a submerged belt of land, 9 geographic miles wide, extending seaward along the coast.

structural basin - A structural basin is a large-scale structural formation of strata formed by tectonic down warping. Structural basins may be sedimentary basins, which are aggregations of sediment that filled a depression; however, many structural basins were formed by tectonic events after the sedimentary units were deposited.

sweet crude - Petroleum is considered "sweet" if it contains less than 0.5% sulfur compared to a higher level of sulfur in sour crude oil. Sweet crude oil contains small amounts of hydrogen sulfide and carbon dioxide.

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tar sands - See "oil sands."

technically recoverable - Those resources producible using currently available technology and industry practices. USGS is the only provider of publicly available estimates of undiscovered technically recoverable oil and gas resources.

tectonic - Pertaining to the structure of the earth's crust.

tight gas - Is natural gas trapped in a highly mixed mineralogy sandstone, shale, or limestone formations which has very low permeability and porosity. While conventional natural gas accumulations, once drilled, contain gas that can usually be extracted quite readily and easily, a great deal more effort, including hydrofracturing, has to be put into extracting gas from a tight formation.

Total Petroleum System (TPS) - the essential elements (source, reservoir, seal, and overburden rocks) and processes (generation-migration-accumulation and trap formation) as well as all genetically related petroleum that occurs in seeps, shows, and accumulations (discovered and undiscovered) whose provenance is a pod or closely related pods of active source rock. 

trap - A geologic feature that permits the accumulation and prevents the escape of accumulated fluids (hydrocarbons) or injected carbon dioxide from the reservoir.

trapping (CO2) - The physical and geochemical processes by which injected carbon dioxide (CO2) is retained in the subsurface. 


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U, V, W, X, Y, Z

unconventional oil accumulation - A "continuous” or "unconventional" oil accumulation means that the oil resource is dispersed throughout a geologic formation(s) rather than existing as discrete, localized occurrences, such as those in conventional accumulations. Unconventional resources often require special technical drilling and recovery methods.

undiscovered - Resources postulated, on the basis of geologic knowledge and theory, to exist outside of known fields or accumulations. Included also are resources from undiscovered pools within known fields to the extent that they occur within separate plays.

unproved reserves - Unproved reserves are based on geologic and/or engineering data similar to that used in estimates of proved reserves; but technical, contractual, economic, or regulatory uncertainties preclude such reserves being classified as proved.

uranium - Uranium (chemical symbol U, atomic number 92) is a silvery metallic element in the actinide series. The heaviest naturally occurring element, uranium is nearly twice as dense as lead and weakly radioactive. It occurs naturally in low concentrations (a few parts per million) in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite.

vitrinite - One of the primary components of coal and most sedimentary kerogen. Vitrinite is a type of maceral, where "macerals" are organic components of coal analogous to the "minerals" of rocks. It is derived from the cell-wall material or woody tissue of plants.

volatile - readily vaporizable

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Acronym Quick List

ANWR - Arctic National Wildlife Refuge
AU - assessment unit
API - American Petroleum Institute
BBO - billions of barrels of oil
BBOE - billions of barrels of oil equivalent
BCF - billion cubic feet
BLM - Bureau of Land Management
BOEM - Bureau of Ocean Energy Management
BSEE - Bureau of Safety and Environmental Enforcement
BTU - British thermal unit
DOE - Department of Energy
DOI - Department of Interior
EIA - Energy Information Administration
EPCA - Energy Policy and Conservation Act
MBO - thousand barrels of oil
MMBO - million barrels of oil
NGL - natural gas liquids
NOGA - national oil and gas assessment
NPRA - National Petroleum Reserve Alaska
OCS - outer continental shelf
PRB - Powder River Basin
TCF - trillion cubic feet
TPS - total petroleum system
TOC - total organic carbon
WLCI - Wyoming Landscape Conservation Initiative



Page Last Modified: Wednesday, December 03, 2014