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.

All | # A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
There are currently 3 names in this directory beginning with the letter O.

Open Ended Valve or Line (OEL)
Any valve having one side of the valve seat in contact with the process fluid and one side open to the atmosphere, either directly or through open piping, (but excluding any pressure relief valve). [13] A line to safely evacuate gas. [12]

Operational emissions
Methane emissions from normal or planned operating activities. This includes release through stacks; blow off valves, pressure release and purging of turbines and emissions due to normal maintenance inspection and control. Operational vents comprise planned venting and purging of pipelines, which is usually done during commissioning, decommissioning, renewal and maintenance of pipelines for safety reasons to prevent the risk of explosions. Pneumatic device emissions are also operational emissions. [11]

Organic Vapour Analyser (OVA)
Portable hydrocarbon detectors that can be utilized to identify methane leaks. An OVA consists of a flame ionization detector (FID) or photoionization detector (PID), which is capable of measuring the organic vapour concentration in air.


[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’