Skip Navigation Links
About Natural Gas
Gas Utility Operations Best Practices Program
Energy Industry Analyses & Statistics
Find Industry Jobs
Find Vendors and Suppliers
Natural Gas Glossary
Operations & Engineering
Resources by Discipline
Residential Construction


A  | B  |  D  |  E  |  F  |  G  |  H  | I  | J  | K  | L  | M 

O  | R  | S  | U  |  V  |  W  |  Y  | Z


A distribution line that serves as a common source of supply for more than one service line.
Main Extension
The addition of pipe to an existing main to serve new customers.
Main System
Mains, Distribution
Pipes transporting gas within service areas to the point of connection with the service pipe.
Mains, Field and Gathering
Mains, Gas
Pipes used to carry gas from one point to another. As contrasted with service pipes, they carry gas in large volume for general or collective use.
Mains, Transmission
Major Natural Gas Company (Pipeline)
Any natural gas company with combined sales for resale and gas transported or stored for a fee exceeding 50 million Mcf at standard conditions in each of the three previous calendar years.
Make Up
To attach, as drill pipe or a string of tools.
Make-Up Air
Make-Up Gas
The contractual right to take gas volumes at a future date that were available but not taken on their designated date as with take-or-pay contracts.
Make-Up Water
Water added to a tank, boiler, or other vessel to maintain a pre-determined liquid level.
Mandatory Carriage
The obligation to carry, for a fee, gas offered by another party. Also known as COMMON CARRIAGE.
An opening into a tank, boiler, furnace, vault, or other equipment through which a person can enter to service equipment; can be sealed with a removable plate or door.
The conduit of an appliance which supplies gas to the individual burners. Also, a pipe to which two or more outlet pipes are connected.
A tube in the shape of a U, partially filled with
A lace-like hood or envelope (sack) of some refractory material which, when placed in position over a flame, gives light by incandescence.
Manufactured Gas
A gas obtained by destructive distillation of coal, by the thermal decomposition of oil, or by the reaction of steam passing through a bed of heated coal or coke. Examples are coal gases, coke or oven gases, producer gas, blast furnace gas, blue (water) gas, or carbureted water gas. The Btu content varies widely.
Marginal Cost
The cost of the next unit if it were purchased. See INCREMENTAL COST.
Market Area
Any area in which the company feels that gas can be sold in the public convenience and necessity to the benefit of the company and stockholders.
Market Out
A gas purchase contract provision which enables a pipeline to get out of its contract based upon changes in the marketability of gas.
Market Potential
In DSM, an estimate of the possible energy savings that would occur because of normal market forces, without the implementation of a DSM program. Compare ACHIEVABLE POTENTIAL, ECONOMIC POTENTIAL and TECHNICAL POTENTIAL.
Market Requirement
Volumes of gas needed by gas consumers and expressed in volume of daily demand and total annual volumes.
Market Sensitive Contract
A contract whose pricing and sales quantity terms can be adjusted to reflect changes in supply and demand conditions.
Market-Based Pricing
The basing of a longer-term contract or rate schedule on published current market prices of competing supplies of natural gas or alternate fuels. Also known as MARKET-RESPONSIVE PRICING.
Market-Responsive Pricing
Entity which sells natural gas it has purchased from a producer or other seller.
Marketer (Broker)
A non-regulated buyer and seller of natural gas.
Marketing Affiliate
A marketing company that has corporate ties to an interstate pipeline, an intrastate pipeline, or a local distribution company.
Marsh Gas
Methane (CH4) the primary constituent of natural gas. Results from the partial decay of plants in swamps.
Massachusetts Formula
A method used to allocate costs incurred by a parent company on behalf of its affiliates to those affiliates. The "Mass Formula" has three parts using the allocation factors (ratios comparing the affiliate to the company as a whole) of gross plant, gross revenues, and labor, which are added together and then divided by three to arrive at a simple average of the three factors. This formula attempts to weight various aspects of each of the affiliates so that a fair distribution of the overhead cost is allocated to each affiliate member. Compare to DISTRIGAS METHOD.
Materials Transportation Bureau (MTB)
An independent office reporting to the Secretary of Transportation of the United States Government, charged with enforcing the Pipeline Safety Act. MTB, among other functions, receives reports of safety-related incidents from gas system operators and periodically issues revisions and interpretations to the Minimum Federal Safety Standard (49 CFR 192).
Maximum Actual Operating Pressure
Maximum Allowable Operating Pressure
Maximum Daily Quantity
The greatest quantity of gas to be received and/or delivered in a twenty-four hour period by the transporting pipeline on behalf of the shipper under terms defined in a contract. See MDQ.
Maximum Day Allocation
Maximum Efficient Rate (MER)
The maximum rate at which oil can be produced without excessive decline of reservoir energy or a loss in ultimate production.
Maximum Gas in Storage
Maximum Transportation Rate
The maximum rate that an open-access transporter may charge for its services. Section 284.7(c) of the Commission's regulations states that maximum rates for both peak and off-peak periods should ration capacity during peak periods and maximize throughput.
Maximum Working Pressure
The maximum actual operating pressure existing in a piping system during a normal annual operating cycle or the maximum pressure for safe operation of a system.
The quantity of natural gas occupying a volume of one thousand cubic feet at a temperature of sixty degrees Fahrenheit and at a pressure of fourteen and seventy-three hundredths pounds per square inch absolute.
The term MDQ refers to maximum daily quantity of gas which a buyer, seller, or transporter is obligated to receive or deliver at each receipt or delivery point or in the aggregate as specified in an agreement.
Measuring and Regulating Station
Facilities installed at a given location for measuring and regulating the flow of gas in connection with distribution system operations other than the measurement of gas deliveries to customers.
Mechanical Equivalent of Heat
The conversion factor for transforming heat units into mechanical units of work. One Btu equals 778 foot-pounds.
Mechanical Rig
A drilling rig whose source of power is one or more internal combustion engines.
When the Federal Energy Regulatory Commission (FERC) issued a Notice Of Proposed Rulemaking (NOPR) wherein it served notice of its intention to totally restructure the natural gas industry, the NOPR was referred to as the "Mega" NOPR because of its scope.
A group of organic chemical compounds containing an SH group having distinctive odors in small concentrations is often added to natural or LP gases to warn of leaks. Compare ODORANT.
Merchant Obligation
The buying and gathering of natural gas for resale.
Meter Bar
A metal bar for mounting a gas meter having fittings at the ends of the bar for connecting the inlet and outlet connections of the meter and to which, in turn, the gas service line and house piping are connected.
Meter Book
Book in which successive readings of utility customers' meters are recorded by gas utility meter readers. The difference between successive readings is the gas consumption for the period.
Meter Class
A designation for a range of meter capacity. The class for a given type of meter is determined by its minimum capacity based on 0.6 specific gravity gas at 0.5 inches of water column differential pressure, under specified test conditions. The capacity so determined must equal or exceed the class designation, but be less than the next higher class.
Meter Cock
Meter Density
The number of meters per unit of area or per unit length of distribution main.
Meter Index (Meter Register)
That part of a meter which indicates the volume of gas passed through the meter.
Meter Manifold
Gas piping between gas service line and meter. Also, gas piping supplying two or more meters.
Meter Seal
A metal wire or tape seal attached to a gas meter or a service stop in such a way as to prevent its being opened by an unauthorized person.
Meter Set (Meter Installation)
The meter and appurtenances thereto, including the meter, meter bar, and connected pipe and fittings. Also called METER SET ASSEMBLY.
Meter Stop
A shut-off valve located on the inlet side of the meter. It may be integral with the meter bar.
Meter Swivel
The fitting that connects to the inlet and the outlet of a small gas meter.
Meter, Diaphragm
A meter which uses a flexible diaphragm in a bellows-type arrangement to measure the volume of gas. Compare METER, POSITIVE DISPLACEMENT.
Meter, Gas
An instrument for measuring and indicating or recording the volume of gas that has passed through it.
Meter, Hard Case
A meter in which the case is made of an inflexible metal, such as iron or aluminum.
Meter, Orifice
A meter using the differential pressure across an orifice plate as a basis for determining volume flowing through the meter. Ordinarily, the differential pressure is charted.
Meter, Positive Displacement
An instrument which measures volume on the basis of filling and discharging gas in a chamber. Compare METER, WET TEST.
Meter, Proportional
A meter which measures automatically a proportional part of the volume flowing past a metering point.
Meter, Rotary Displacement
An instrument which measures volume by means of rotating impellers, matching gears, or sliding vanes.
Meter, Temperature Compensated
One in which the measurement of gas volume is automatically corrected for variation in gas temperature.
Meter, Tinned Case
A meter in which the case is made of tinned sheet metal, with joints sealed with tin solder.
Meter, Turbine
A velocity measuring device in which the flow is parallel to the rotor axis and the speed of rotation is proportional to the rate of flow. The volume of gas measured is determined by the revolutions of the rotor and converting them to a continuously totalized volumetric reading.
Meter, Venturi
A meter using the static pressure differential between the meter entrance and the throat as a basis for determining volume flowing through the meter.
Meter, Wet Test
A positive displacement meter using a liquid, usually water, as a sealant and as one side of the displacement chamber, to measure gas volume.
Catalytic upgrading of synthetic fuel gas to high Btu. Hydrogen and carbon monoxide react to form methane.
Methane (CH4)
The first of the paraffin series of hydrocarbons. The chief constituent of natural gas. Pure methane has a heating value of 1012 Btu per cubic foot.
The second stage of the anaerobic conversion of a biomass feedstock to methane. The first stage converts the feedstock to an acid such as acetic acid. This acid is then converted to methane by microorganisms in the methanogenesis stage.
Methyl ethyl ketone (MEK)
An organic solvent widely used for preparing solvent cements, formula C2H5COCH3.
The movement of oil, gas or water through porous and permeable rock.
Mile Post Location
The location in miles along a pipeline from 0.00, usually expressed in hundredths of a mile.
One tenth of a cent.
Mined Cavern
A storage concept for LNG that is under investigation in which LNG is stored in the earth in caverns mined in various rock formations (e.g., limestone, shale, chalk, granite, dolomite) by conventional or solution mining. Both insulated and uninsulated cavern storage have been proposed. The concept has been used successfully with liquefied petroleum gases (LPG).
Mineral Right
The ownership of the minerals under a given surface with the right to enter thereon, mine, and remove them. It may be separated from the surface ownership, but if it is not so separated by distinct conveyance, the latter includes it.
Minimum Bill Clause (Minimum Charge)
A clause in a rate schedule which provides that the charge for a prescribed period shall not be less than a specified amount.
Minimum Commodity Bill
Provisions in a rate schedule (jurisdictional) or contract (nonjurisdictional) requiring customers to purchase minimum annual volumes of gas or, under certain circumstances, pay the fixed cost portion of the commodity rate on any volumes which fall below the minimum volume level. The Federal Energy Regulatory Commission has stated in Atlantic Seaboard the three factors needed to justify a minimum bill: (1) protecting the pipeline against the risk of not recovering the fixed costs in the commodity component; (2) protecting full requirements customers from bearing a disproportionate share of the fixed costs resulting from swings off the system by partial requirements customers; and (3) protecting customers from take-or-pay liabilities that the pipeline might otherwise bear.
Minimum Federal Safety Standard--Part 192
This refers to Title 49, Part 192, of the code of Federal Regulations and contains the legal minimum requirements for gas transportation within the United States.
Minimum Transportation Rate
The minimum rate which an open-access transporter may charge for service. Section 284.7(d) (4) (ii) states that any minimum rate must be based on the average variable costs which are properly allocated to the service to which the rate applies.
Minor Items
(Definition taken from the FERC Uniform System of Accounts, effective April 1, 1986). "Minor Items of Property" means the associated parts or items of which retirement units are composed ("Definitions" Item 18).
Mixed Gas
Fuel gas in which natural or LP gas is mixed with manufactured gas.
The combination of mixer head, mixer throat, and mixer tube. Mixer Head. That portion of an injection type burner, usually enlarged, into which primary air flows to mix with the gas stream. Mixer Throat. That portion of the mixer which has the smallest cross sectional area and which lies between the mixer head and the mixer tube. Mixer Tube. That portion of the mixer which lies between the throat and the burner head.
Mixer Face
The air inlet end of the mixer head.
Mixture, Lean
A gas-air mixture of which the air content is more than adequate for complete combustion and the resultant combustion gases will contain an excess of oxygen.
Mixture, Rich
A gas-air mixture of which the air content is not sufficient for complete combustion.
A thermal unit of energy equal to 1,000,000 Btus, that is, the equivalent of 1,000 cubic feet of gas having a heating content of 1,000 Btus per cubic foot, as provided by contract measurement terms. See DEKATHERM.
A million cubic feet. See CUBIC FOOT.
Modified Btu Method
A modification of the Btu Method of allocating costs between different operations or between different products.
Modified Fixed Variable
Modified Fixed-Variable (MFV) Method
A method for classifying fixed costs among demand and commodity charges in which all fixed costs except return on equity capital and related income tax items are classified to the demand charge. This method generally replaced other methods used by the Commission for classifying demand costs when first approved in the mid-1980s. The MFV method of cost classification usually is accompanied with a rate design methodology which employs a two-part (D-1 and D-2) demand and a commodity rate structure. See FIXED-VARIABLE METHOD, ATLANTIC-SEABOARD METHOD, CLASSIFICATION UNITED METHOD and VOLUMETRIC RATES.
Modified Seaboard Method
Molecular Weight
The sum of the atomic masses of the elements forming the molecule. In high polymers the molecular weights vary so widely they must be expressed as averages.
Molecular Weight Distribution
The ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) gives an indication of the distribution.
Molecular Weight, Weight Average (Abbreviation Mw)
The sum of the total weight of molecules of each size multiplied by their respective weights divided by the total weight of all molecules.
To sense the presence of a flame. The device which does this is called a flame monitor. Also, to analyze and record various desired and undesired components of an atmosphere, or stream of flowing gas or fluid.
Monitoring Regulator
A pressure regulator set in series with a control pressure regulator for the purpose of automatically taking over the control of the pressure downstream in case that pressure tends to exceed a set maximum.
Monthly Service
A predefined monthly period in which daily services are summarized for invoicing and imbalance statements. Typically billing months are not calendar months, except for large volume and special use customers. See CYCLE BILLING.
Rating Quality Description:
Moody's Bond Ratings
Moody's Bond Yield (Annual Averages of Monthly Yie
Represents the average yield on 40 operating utility companies' bonds (10 each of Class Aaa, Aa, A, and Baa) as determined and rated by Moody's Investors Service. This "yield" is the arithmetic average of 12 months and is calculated on the basis of market price, interest rate, and on being "held to maturity".
Moody's Stock Quality Groups
Preferred and Common Stocks: High Quality - High quality by all standards. Good Quality - Possesses many favorable high-grade investment attributes. Medium Quality - Medium grade equity securities.
Motion Rates
Rates placed into effect subject to refund at the end of the five month suspension period by the motion of the company. These rates are not necessarily the same as the company's filed rates.
Moving-Bed Gasifier
A gasifier in which coke is fed into the top keeping the gasifier essentially full when operating. Ash is removed at the bottom while the coal is consumed as it moves downward through the bed.


Join the Energy Conversation