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 5 names in this directory beginning with the letter C.

Calibrated vent bag
Non-elastic bag of known, fixed volume when fully inflated. (Note - Measurement is made by timing the bag expansion to full capacity. The temperature of the gas is measured to allow correction of volume to standard conditions. Additionally, gas composition should be analysed to determine the methane content of the vented gas because in some cases air may also be entrained in the vent, resulting in a mixture of gas and air. Bags of various sizes and known volume are available as calibrated during manufacture. Calibrated vent bags are made from antistatic plastic with a neck shaped for easy sealing around a vent pipe.)

Calibration gas
Reference gas or gas mixture used to adjust the meter reading of a measurement instrument to a known value. The calibration gas is generally the reference compound at a predefined concentration and is traceable to primary standards.

A part or element of a larger whole. In the context of equipment leaks, components are individual sealed surfaces on pressurized equipment such as flanges, valves, connections, pressure relief valves, open ended lines, etc. [12] (Note - Please see definition of Granularity terms below.)

Area of contact between two or more linked parts, axially or radially, normally sealed by mechanical means in order to keep tightness. [12]

Control valve
Modulating valve that controls either the flow rate, liquid level, or pressure in process equipment. In the latter case, it is often referred to as a (pressure) regulator. [12] (Note - Typically, high pressure gas from the pipeline is used as the supply medium needed to energize the valve actuator.)


[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’