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Glossary of Terms 



ABANDONED WELL – A well not in use because it was a dry hole originally or ceased to produce. Statutes and regulations in many states require the plugging of abandoned wells to prevent the seepage of oil, gas or water from one stratum of underlying rock to another.

ACCUMULATION OF HYDROCARBONS – Accumulation in the highest permeable areas of a reservoir due to hydrodynamics.

ACID TREATMENT – A refining process in which unfinished petroleum products such as gasoline, kerosene, diesel fuels  are treated with sulfuric acid to improve color, odor, and other properties.

ACOUSTIC LOG – A generic term for a well log that displays any of several measurements of acoustic waves in rocks exposed in a borehole.

AGE – A portion of geologic time when rocks of a specific stratigraphic unit were deposited, or designated a particular segment of the geologic time scale.

API GRAVITY – The measure of the density or gravity of liquid petroleum products in the United States. API gravity is expressed in degrees, 10 degrees API being equivalent to 1.0,  the specific gravity of water.

ANTICLINE – An upwardly convex fold with limbs that dip away from the axial position.

APPRAISAL DRILLING – Wells drilled in the vicinity of a discovery or wildcat well in order to evaluate the extent and the importance of the find.

AREA OF MUTUAL INTEREST – An area, usually outlined on a plat attached to a farmout agreement or described in an exhibit, that allows both parties the first right of refusal on leases acquired by either party after the agreement is executed.

ASSIGNMENT – In oil and gas usage, assignment is a transfer of a property or an interest in an oil or gas property; most commonly, the transfer of an oil or gas lease.

ASSOCIATED GAS – Gas that occurs with oil, either as free gas or in solution. Gas occurring alone in a reservoir is unassociated gas.


BACK-IN-PROVISION – A term used to describe a provision in a farmout agreement whereby the person granting the farmout  has the option to exchange a retained override for a share of the working interest.

BAR – An elongate detrital ridge, mound or bank deposited by marine waves and currents, or rivers and streams.

BASIN – A low area with no exterior drainage. Often an area of sedimentary deposition; lake basin; marine basin.

BASKET PRICE – The blanket or average price of crude oil on the world market. For example, the basket price of $20.00/bbl. could mean average price of average gravity. Lower-gravity crude with high-transit cost would bring less than $20.00, and conversely, higher gravity crude with low sulfur and close to market would be a premium – a basket of crude oils of differing gravities, sulfur content, sweet and sour.

BATTERY – Two or more tanks connected together to receive oil production on a lease.

BBL – Barrel of oil.

BED – A stratum or layer of rock.

B.H.T. – Bottom-hole temperature. In deep wells, 15,000 feet and deeper, bottom-hole temperatures are above the boiling point of water, ranging up to 400 degrees Fahrenheit. At these depths and temperatures, water-base drilling muds can not be used, only oil-based.

BIT, ROTARY – The tool attached to the lower end of the drillpipe; a heavy steel head equipped with various types of cutting or grinding teeth.  A hole in the bottom of the drill permits the flow of drilling mud being pumped down through the drillpipe to wash the cuttings to the surface and also cool and lubricate the bit.

BIT, SPUDDING – A bit used to start the borehole; a bit that is some variation of the fishtail or drag bit, one used in soft, unconsolidated, near-surface material.

BLINDPOOL  – Money put into a drilling fund that is held by the fund managers until likely prospects for drilling are found or come along. The rationale for the blind fund is that with ready money, the fund managers can act quickly when good opportunities for investment arise.

BLOWING A WELL – Opening a well to let it blow for a short period to free the well tubing or casing of accumulations of water, sand, or other deposits.

BLOWOUT – Out-of-control gas and/or oil pressure erupting from a well being drilled; a dangerous, uncontrolled eruption of gas and oil from a well.

BLOWOUT PREVENTER – A stack or an assembly of heavy-duty valves attached to the top of the casing to control well pressure; commonly referred to as a "Christmas Tree".

BONUS – Usually, the bonus is the money paid by the lessee for the execution of an oil and gas lease by the landowner.  This may be in the form of an overriding royalty reserved to the landowner in addition to the usual one-eighth royalty.

BOREHOLE – The hole in the earth made by the drill; the uncased drill hole from the surface to the bottom of the well.

B.P.D. – Barrels per day.

B.P.M. – Barrels per minute. The pumping rate of small pumps.

BUTANE – A hydrocarbon fraction; at ordinary atmospheric conditions, butane is a gas but it is easily liquefied; one of the most useful L.P.-gases.


CALCAREOUS – Rock or other material containing up to 50 percent calcium carbonate.

CAP A WELL – To control a blowout by placing a very strong valve on the wellhead.

CAP ROCK – (Salt Dome)- An anhydrite, gypsum, calcite and sulfur body over the top of a salt dome.

CARRIED WORKING INTEREST – A fractional interest in an oil and gas property conveyed or assigned to another party by the operator or owner of the working interest. In its simplest form, a carried working interest is exempt from all costs of development and operation of the property. However, the carried interest may specify “to casing point”, “to setting of tanks”, or “through well completion”. If the arrangement specifies through well completion, then the carried interest may assume the equivalent fractional interest of operating costs upon completion of the well. There are many different types of carried interests, the details varying considerably from arrangement to arrangement.

CASING – The metal pipe lining placed in a well to protect the well bore from caving and fluid contamination.

CASING POINT – A term that designates a time when a decision must be made whether casing is to be run and set or the well abandoned and plugged. In a joint operating agreement, casing point refers to the time when a well has been drilled to objective depth, tests made, and the operator notifies the drilling parties of his recommendation with respect to setting casing and a production string and completing the well.

CHANNEL – A river bed. A place through which a current (marine) can flow such as between two sand bars.

CHRISTMAS TREE – (1) An assembly of valves mounted on the casinghead through which a well is produced. The Christmas tree also contains valves for testing the well and for shutting it in if necessary. (2) A subsea production system similar to a conventional land tree except it is assembled complete for remote installation on the seafloor with or without diver assistance. The marine tree is installed from the drilling platform; it is lowered into position on guide cables anchored to foundation legs implanted in the ocean floor.

CLEAVAGE – Mineral parting along consistent zones of weakness in its molecular structure. A diagnostic mineral physical property.

CONDENSATE – A term used to describe light liquid hydrocarbons separated from crude oil after production and sold separately.

COMPLETION – To finish a well so that it is ready to produce oil or gas. After reaching total depth (T.D.), casing is run and cemented; casing is perforated opposite the producing zone, tubing is run, and control and flow valves are installed at the wellhead.

COMPLETION FUNDS – Completion funds are formed to invest in well completions, to finance the completing and equipping of a potentially productive well. After a well is drilled into a productive formation, there remain the costs of setting pipe, (casing the well); perforating, testing, acidizing, or fracturing the formation; and running production tubing and installing pumping equipment, separators, stock tanks, etc. The operator who drills the well may not have the financial resources to complete the well, so he may sell part or all of his interests to a completion fund.

CONTOUR INTERVAL – Difference in value between adjacent contour lines.

CONTOUR LINE – A line of specific value which connects points of the same numerical value.

CONTOUR MAP – A map of contour lines, spaced by a contour interval to illustrate topography, structure, etc.

CORE SAMPLE – A solid column of  rock, usually from 2 – 4 inches in diameter, taken from the bottom of a well bore as a sample of an underground formation. Cores can also taken in geological studies of an area to determine the oil and gas prospects.

CROSS-SECTION - A diagram along a specific, usually vertical plane or surface, which shows the distribution of structural and/or stratigraphic features.

CRUDE OIL – A mineral oil consisting of a mixture of hydrocarbons of natural origin, yellow to black in color, of variable specific gravity and viscosity.


DENSITY – Mass per unit volume: grams per cubic centimeter, pounds per cubic foot.

DEPOSITIONAL SEQUENCE – The conditions under which deposition occurs; fluvial, marine, glacial, deltaic, etc.

DERRICK – A wooden or steel structure built over a wellsite to provide support for drilling equipment and a tall mast for raising and lowering drillpipe.

DEVELOPMENT WELLS – Wells drilled in areas already proved to be productive.

DIP – The departure normal to the strike in degrees of an inclined plane from the horizontal.

DISCOVERY WELL – An exploratory well that encounters a new and previously untapped petroleum deposit; a successful wildcat well.

DOWNHOLE – A term to describe tools, equipment, and instruments used in the well bore.

DOWNSTREAM – A segment of the oil industry. Term is used to refer to all petroleum activities from the processing of refining crude oil into petroleum products to the distribution, marketing, and shipping of the products. The opposite of downstream is upstream.

DRILLING PERMIT – In states that regulate well spacing, a drilling permit is the authorization to drill at a specified location.

DRILLING PROGRAM – An integrated schedule of drilling parameters to most effectively drill an oil or gas well.

DRY GAS – Natural gas from the well that is free of liquid hydrocarbons; gas that has been treated to remove all liquids making it suitable for shipping in a pipeline.

DRILL STEM TEST – A test to determine production potential of a particular formation interval using testing equipment installed in the drill string.

DRY HOLE – Any well that does not produce oil or gas in commercial quantities. A dry hole may flow water, gas, or even oil, but not in amounts large enough to justify production.


EFFECTIVE POROSITY – The percent of the total volume of rock that consists of connecting pores or interstices.

ELECTRIC LOG  -An electrical survey made on uncased holes. A special tool is lowered into the hole which ejects an electrical current into the rock and records its resistance to the current.

EROSION – Removal of rock material to another place by one or several transportation agencies.

EXPLORATION - The search for reservoirs of oil and gas, including aerial and geophysical surveys, geological studies, core testing and drilling of wildcat wells.


FARMOUT -An agreement whereby the owner of a lease who does not wish to drill at the time agrees to assign the leasehold interest to a third party who does wish to drill.

FAULT -A break in the earth's crust along which rocks on one side have been displaced (upward, downward, or laterally) relative to those on the other side.

FLOWING WELL -A well capable of producing oil or gas by its own energy without the aid of a mechanical pump.

FOLD – A bent or curved stratum, cleavage plane or foliation.

FOSSIL – Preserved plat or animal material.

FOSSIL FUEL – Any naturally occurring fuel of an organic nature formed by the decomposition of plants or animals; includes coal, natural gas, and petroleum.

FRACING - The process of pumping fluids into a productive formation at high rates of injection to hydraulically break the rock. The "fractures" which are created in the rock act as flow channels for the oil and gas to the well.

FIELD POTENTIAL – The producing capacity of a field during a 24-hour period.

FLARE – (1) To burn unwanted gas through a pipe or stack (Under conservation laws, the flaring of natural gas is illegal.) (2) The flame from a flare; the pipe or the stack itself.

FOSSIL ENERGY – Energy derived from crude oil, natural gas, or coal.


GAS – “Any fluid, combustible or noncombustible, which is produced in a natural state from the earth and which maintains a gaseous or rarified state at ordinary temperature and pressure conditions”. Code of Federal Regulations, Title 30, Mineral Resources, Chap. II, Geological Survey, 221.2 

GAS CAP – The portion of an oil-producing reservoir occupied by free gas; in a free state above an oil zone.

GAS SHOW – A gas indication in well cuttings.

GAS WELL - A well that produces natural gas which is not associated with crude oil.

GEOLOGY – The science of the history of the Earth and its life as recorded in rocks

GEOPHYSICS – Quantitative Earth study using physical techniques.

GLACIER – A slow moving gravity motivated ice accumulation.

GRAVITY – Specific gravity. The ratio between equal volumes of water and another liquid, where the weight of the water is given a value of 1. The specific gravity of oil is given as API Gravity.

GRAVITY MAP – A map contoured on gravity units which illustrates areas of positive and negative gravity generated by density contrasts.


HYDROCARBONS – Organic chemical compounds of hydrogen and carbon atoms. There are a vast number of these compounds, and they form the basis of all petroleum products. They may exist as gases, liquids, or solids. An example of each is methane, hexane, and asphalt.

HYDROSTATIC PRESSURE – The pressure caused at any point in a resting body of water.


IDC - (Intangible Drilling Costs) All cost incurred in drilling a well other than equipment or leasehold. These expenses are 100% tax deductible even if the well is productive.

IGNEOUS ROCK – Rock that has crystallized from magma (molten material).

IP - (Initial Production) Production from a well is generally broken down into three categories: a. Flush or Initial b. Settled c. Stripper. It is important to realize that a well cannot maintain the flow rates it made during the first stages of its life.



KELLY BUSHING – The sheave system that fits into the rotary table and drives the kelly and the drill string of rotary drilling equipment.


LIGHT ENDS – The more volatile products of petroleum refining, e.g., butane, propane, and gasoline.

LIMESTONE – Lithified calcium carbonate

LIQUIFIED  NATURAL GAS (LNG) – Natural gas liquified either by refrigeration or by pressure.

LIQUIFIED  PETROLEUM GAS (LPG) – A mixture of butane, propane, and other light hydrocarbons derived from refining crude oil. At normal temperature it is a gas but can be cooled or subjected to pressure to facilitate storage and transportation.


MAGMA – Molten Rock.

METAMORPHIC ROCK – Mineralogically, physically, chemically and structurally changed rock.

METHANE – Odorless, colorless, inflammable natural gas.

MINERAL – A naturally occuring inorganic substance with a definite chemical composition, a definite crystal structure and physical properties that vary within predicable limits.

MUD – (drilling) Aqueous mixture of a variety of fine-grained components used to lubricate drilling operations, recover cuttings and stabilize the drill hole.


NATURAL GAS – Petroleum in gaseous form consisting of light hydrocarbons often found in association with oil. Methane is the most dominant component.

NET PRESENT VALUE – A sophisticated capital budgeting technique; found by subtracting a project’s initial investment from the present value of the cash inflows discounted at a rate equal to the firm’s cost of capital.

NON-COMMERCIAL - A well that is not capable of producing enough oil to pay for the drilling.

NRI - (Net Revenue Interest) That percent of the production revenue allocated to the working interest after first deducting proceeds allocated to royalty and overriding interest.


OFFSET WELL – (1) A well drilled on the next location to the original well. The distance form the first well to the offset well depends upon spacing regulations and whether the original well produces oil or gas. (2) A well drilled on one tract of land to prevent the drainage of oil or gas to an adjoining tract where a well is being drilled or is already producing.

OIL - A liquid hydrocarbon.

OIL BEHIND THE PIPE – Refers to oil and gas sands or formations knowingly passed through, never produced. Such formations usually were of low permeability  that, say 15 years ago, were uneconomical to produce when oil was around $5 or less a barrel. Other times formations would be purposely ignored because the operator was going deeper for bigger game, so the less-spectacular, plain-Jane sands were cased off.

OIL FIELD – Two or more closely related oil-producing areas on the same geological feature.

OIL GRAVITY - The most widely used indicator of a crude oil's worth to the producer is its API gravity. Normally, the price which a producer receives for his oil depends on its gravity, the less dense oils (higher API gravity) being the most valuable. This price schedule is based on the premise that the lighter oil contains higher percentages of the more valuable products such as gasoline.

OIL IN PLACE – Crude oil estimated to exist in a field or a reservoir. Oil in the formation not yet produced.

OIL & GAS LEASES - A contract between an oil operator and a landowner which gives the operator the right to drill for oil and gas on his property for a consideration.

OIL SHOW – An indication of oil in well cuttings.

OPERATOR – Term used to describe a company appointed by venture stake holders to take primary responsibility for day-to-day operations for a specific plant or activity.

OPEN HOLE – An uncased well bore; the section of the well bore below the casing.

OPEN-HOLE LOGGING – Logging operations in an uncased well bore.

OPERATING EXPENSE - The expenses incurred through the operation of producing properties.

ORGANIZATION OF PETROLEUM EXPORTING COUNTRIES (OPEC) – Oil producing and exporting countries in the Middle East, Africa, and South America that have organized for the purpose of negotiating with oil companies on matters of oil production, prices, and future concession rights.



PALEONTOLOGY - The science that concerns the life of past geologic periods, especially fossil forms and the chronology of the earth.

PAYOUT - When the costs of drilling, producing and operating have been recouped from the sale of products on a well.

PERFORATING GUN – A special tool used downhole for shooting holes in the well’s casing opposite the producing formation. The gun, a steel tube of various lengths, has steel projectiles placed at intervals over its outer circumference, perpendicular to the gun’s long axis. When lowered into the well’s casing on a wireline opposite the formation to be produced, the gun is fired electrically, shooting numerous holes in the casing that permit the oil or gas to flow into the casing.

PERMEABILITY - A measure of the ease with which a fluid flows through the connecting pore spaces of rock or cement.

PETROLEUM MIGRATION – Movement of petroleum through permeable rock media from locality of generation.

PINCHOUT – The disappearance or “wedging out” of a porous, permeable formation between two layers of impervious rock.

PIPELINE GAS – Gas under sufficient pressure to enter the high-pressure gas lines of a purchaser; gas sufficiently dry so that liquid hydrocarbons – natural gasoline, butane, and other gas liquids usually present in natural gas – will not condense or drop out in the transmission lines.

POINT BAR – Coarse-grained, often cross-bedded, river channel deposits on the inside, low velocity part of a meander.

PORE SPACE – Voids in rock materials.

POROSITY – The amount of void space in rock materials.

PLUG – To fill a well’s borehole with cement or other impervious material to prevent the flow of water, gas or oil from one strata to another when a well is abandoned.

PLUGGING A WELL – To fill up the borehole of an abandoned well with mud and cement to prevent the flow of water or oil from one strata to another or to the surface.

POROSITY - A measure of the relative volume of void space in rock to the total rock volume.

PROVEN RESERVES - Oil and gas which has not been produced but has been located and is recoverable.

PUMPING UNIT – A pump connected to a source of power; an oil-well pumping jack; a pipeline pump and engine.



REAL ESTATE INVESTMENT TRUSTS(REITs) - A trust or association that invests in a variety of real estate. REITs are managed by one or more trustees, like a mutual fund, and trade like a stock. No federal income tax needs to be paid by the trust if 75% of the income is real-estate related and 95% of the income is distributed to investors.

REEF RESERVOIR – A type of reservoir trap composed of rocks which are made up of the skeletal remains of marine animals. Reef reservoirs are often characterized by high initial production that falls off rapidly.

RESERVOIR – A porous, permeable sedimentary rock formation containing quantities of oil and/or gas enclosed or surrounded by layers of less-permeable or impervious rock.

RESERVOIR PRESSURE – Pressure in a subsurface petroleum-bearing rock, due to overburden thickness, deformation, fluid column, etc.

RETURN ON CAPITAL EMPLOYED (ROCE) – ROCE is a measure of how productively a company manages its refining, marketing, and transportation assets. ROCE is the ratio of operating profits generated to the amount of operating capital invested.


ROCK – A naturally occurring aggregate of minerals of igneous, sedimentary, or metamorphic origin.

ROYALTY, LANDOWNER’S – A share of gross production of oil and gas, free of all costs of production. Occasionally, the term is used to describe an interest in production created by the landowner outside the lease and distinguished from the conventional lessor’s royalty. In this case the landowner’s royalty, outside of the lease, may have any specified duration.


SALT WATER DISPOSAL WELL - Many wells produce salt water while producing oil.  The disposal of this water is a problem to an operator because of pollution.  The best solution to the problem is to pump the waste back into a formation that is deep enough not to pollute shallow water sands. 

SANDSTONE – A clastic sedimentary rock of sand-size quartz grains.

SCOUT TICKETS – A written report of wells drilling in the area. The reports contain all pertinent information – all that can be found out by the enterprising oil scout; operator, location, lease, drilling contractor, depth of well, formations encountered, results of drillstem tests, logs, etc.

SECONDARY RECOVERY - A broad term encompassing any method of extracting oil from a reservoir after a well or field has exhausted its primary production.

SEDIMENTARY ROCKS - Rock is generally classified in one of three categories:  a. Sedimentary;  b. Igneous;  c. Metamorphic. Sedimentary rocks are composed of materials that were transported to their present position by wind or water. Sandstone, shale and limestone are sedimentary rocks.

SEISMIC DATA – Detailed information obtained from earth vibration produced naturally or artificially (as in geophysical prospecting).

SEISMIC METHOD – A method of geophysical prospecting using the generation, reflection, refraction detection, and analysis of sound waves in the earth.

3-D SEISMIC PROGRAM – Seismic surveys shot from surfaces to map underground stratigraphy; to profile the underlying strata in search of geological faults needed for the accumulation of oil and gas.

SET CASING – To cement casing in the hole. The cement is pumped downhole to the bottom of the well and is forced up a certain distance into the annular space between casing and the rock wall of the drill hole. It is then allowed to harden, thus sealing off upper formations that may contain water. The small amount of cement in the casing is drilled out in preparation for perforating to permit the oil to enter the casing.

SHALE – A very fine-grained sedimentary rock formed by the consolidation and compression of clay, silt, or mud.

SHOT HOLE – A small-diameter hole, usually drilled with a portable, truck-mounted drill, for planting explosive charges in seismic operations.

SHUT IN – To close the valves on a well so that it stops producing.

SOUR GAS – Natural gas containing chemical impurities, a notable hydrogen sulfide or other sulfur compounds that make it extremely harmful to breathe even small amounts.

SPOT PRICE – The price for a one-time open market transaction for immediate delivery of a specific quantity of product at a specific location where the commodity is purchased “on the spot” at current market rates.

STRATIGRAPHIC TEST – A test well drilled to obtain information on the thickness, lithology, porosity, and permeability of the rock layers drilled through or to locate a key bed.

STRUCTURAL TRAP – A petroleum trap formed by deformed geologic feature.

STRIKE – The horizontal line of intersection between a dipping surface and a horizontal plane.

STRIPPER WELL - The final state in the life of a producing well.

STRUCTURAL TRAP - A fold or break (or both) in the earth's crust which creates an impervious trap for oil and gas. 

SUCKER ROD – Steel rods that are screwed together to form a “string” that connects the pump inside a well’s tubing downhole to the pumping jack on the surface.

SURFACE PIPE - Pipe which is set with cement through the shallow water sands to avoid polluting the water and keep the sand from caving in while drilling a well.

SWEET CRUDE – Crude oil containing very little sulfur.

SWEET GAS – Natural gas free of significant amounts of  hydrogen sulfide  when produced.

SYNCLINE – A downwardly convex fold with limbs that dip toward the axis.


TESTING - When each new well is competed, a series of tests are run on the well.   The various tests are used to estimate the daily deliverability, payout, and reserves.

TIGHT HOLE – A well about which information is restricted for security or competitive reasons.

TOTAL DEPTH (T.D.) – The depth of a well when drilling is completed. Total depth of a well is the vertical distance from the rig floor to the bottom of the hole.

TRAP – A type of geological structure that retards the free migration of oil and concentrates the oil in a limited space.

TUBING - Small diameter pipe which is installed in the casing.  Oil is produced through tubing because it increases the viscosity of fluid and a well's flow capabilities.

TURNKEY CONTRACT - A contract in which an operator or drilling contractor agrees to furnish all labor and materials necessary to drill a well to a certain depth or stage of completion for a specified sum of money. 



UNCONFORMITY - Lack of continuity in deposition between rock strata in contact with one another, corresponding to a gap in time of the stratigraphic record.

UPLIFT - A redundant term to describe a structurally high portion of the crust.

USGS - United States Geological Survey.


VESICULAR - Containing small cavities that are visible to the naked eye. A vesicular rock is a rock that contains small cavities.

VISCOSITY - The resistance of fluid to flow. A high viscosity fluid will not flow as easily as a low viscosity fluid .


WALKING BEAM - The horizontal steel member of a beam pumping unit that has rocking or reciprocating motion.

WASHOUT - A larger diameter portion of a well bore caused by drilling mud removal of soft material.

WATER FLOODING - A secondary recovery method for the production of oil from a formation.   Oil will float on water.  When water is injected into some formations, the oil will float or be washed to the surface, thereby, increasing the amount of production from a well or field.

WELL - A hole drilled in the ground to produce water or petroleum.

WELL BORE - The three-dimensional, circular perforation that results from drilling a well.

WELL COMPLETION – The work of preparing a newly drilled well for production. This is a costly procedure and includes setting and cementing the casing, perforating the casing, running production tubing, hanging the control valves (nippling up the production tree, i.e., Christmas tree), connecting the flow lines, and erecting the flow tanks or lease tanks.

WELL HEAD - The equipment installed at the surface of the wellbore.

WELL LOGGING – Recording information about the surface formation, the nature and extent of the various downhole rock layers. Also included are records kept by the driller, the record of cuttings, core analysis drillstem tests, and electric, acoustic, and radioactivity logs.

WEST TEXAS INTERMEDIATE (WTI) - Refers to West Texas Intermediate crude oil. The WTI spot price of crude is reported from Cushing, Oklahoma.

WHITE OIL – A colloquial term for condensate, gas condensate, casinghead gasoline.

WILDCAT - A well that is drilled one or more miles from a proven well.

WORKING INTEREST - A working interest in an oil or gas property is one that is burdened with the cost of development and operation of the property, such as the responsibility to share expenses of drilling completing or operating an oil and gas property, according to working or operating mineral interest in any tract or parcel of land. Rights to overriding royalties, production payments, and the like do not constitute working interests because they are not burdened with the responsibility to share expenses of drilling, completing, or operating oil and gas property.

WORKING INTEREST, FULL-TERM – A working interest that lasts as long as the well or the lease is productive; as long as oil and gas are produced in quantities that make the well economic to operate.

WORKOVER – Operations on a producing well to restore or increase production. Tubing is pulled and the casing at the bottom of the well is pumped or washed free of sand that may have accumulated.

WRITE-OFFS - That portion of an oil investment which is deductible for tax purposes.