To support the industry and stakeholders in the use of consistent terminology, Ipieca, IOGP, GIE and MARCOGAZ prepared this methane emissions glossary covering the whole natural gas value chain.

Intended for policymakers and regulators working on methane regulation in Europe, this glossary will be updated to reflect new legislation and technologies.

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There are currently 7 names in this directory beginning with the letter M.

Main lines of distribution
Pipework in a gas supply system to which service lines are connected. [2]

Methane emission
Any release of methane to the atmosphere, whatever the origin, reason and duration. [12]

Methane emission detection
Process of identification of methane emissions from potential sources, without the measurement of the mass quantity (flow rate, e.g. kg/h). Several devices, screening instruments and methodologies are available to detect methane emissions, including optical gas imaging cameras, laser leak detectors, portable analysers (OVAs, TVAs), soap bubble screening and/or AVO methods. Some of these are able to detect and provide a concentration level (volume, e.g. ppmv) that can be used to estimate the mass emission (e.g. by applying specific emission factors or correlation equations available from literature). [8]

Methane emission programme
The set of methods chosen by a gas company for identifying, detecting, measuring and quantifying methane emissions. The program may include several screening and surveying technologies and techniques, as well as various quantification techniques to determine the rate of emissions from each detected source. The program summarizes and tracks emissions. [15]

Methane flux
The rate of mass flow of methane through a unit area perpendicular to the wind flow direction. Units of measure are preferably expressed in g CH4/m2 /yr.

Methane intensity
The ratio of methane emissions (numerator) over a selected variable (denominator).
(Note - A methane intensity prevalently used is total methane emissions emitted from an asset, area or value chain (numerator) divided by well production volume, facility throughput, area production volume or gas transported or distributed (denominator) and reflected as a percentage.)

Methane measurement
The process of taking a reading of a methane emission. Measurement can be of any variable (volume, concentration, mass, frequency and so on) that allows for detection or for an estimate of emission rate.


[1] Directive 2009/73/EC of the European Parliament and of the Council of 13 July 2009

[2] EN-12186 – Gas infrastructure – Gas pressure regulating stations for transmission and distribution – Functional requirements

[3] EN-12327 – Gas infrastructure – Pressure testing, commissioning and decommissioning procedures – Functional requirements

[4] EN-12583 – Gas Infrastructure – Compressor stations – Functional requirements

[5] EN-15446 – Fugitive and diffuse emissions of common concern to industry sectors – Measurement of fugitive emission of vapours generating equipment and piping leaks

[6] GIE & MARCOGAZ Report “Potential ways the gas industry can contribute to the reduction of methane emissions”

[7] IPIECA/API/IOGP (2020). Oil and gas industry guidance on voluntary sustainability reporting

[8] IPIECA Methane Glossary

[9] ISO 14532 – Natural gas — Vocabulary

[10] JCGM-100 – Evaluation of measurement data – Guide to the expression of uncertainty in measurement. s.l.: Committee for Guides in Metrology (JCGM/WG 1), 2008

[11] MARCOGAZ – Assessment of methane emissions for gas Transmission and Distribution system operators, 2019 Assessment+of+methane+emissions+for+gas+Transmission+and+Distribution+system+ operator.pdf?t=1602849054

[12] MARCOGAZ – Guidance for using the MARCOGAZ methane emissions reporting template – DSO, TSO, LNG receiving terminals and UGS

[13] MGP Reducing methane emissions: Equipment leaks

[14] MGP Reducing methane emissions: Identification, detection, measurement and quantification

[15] MGP Reducing methane emissions: Transmission, storage, LNG terminals and distribution

[16] Oil and Gas Methane Partnership Technical Guidance Documents

[17] Regulation (EC) No 715/2009 of the European Parliament and of the Council of 13 July 2009

[18] US EPA – ‘Method 21: Determination of volatile organic compound leaks’