Transmission ensures the flow of gas through the high-pressure network between entry points and exit points under appropriate conditions of  quality of service.

The National Natural Gas Transmission Network (Rede Nacional de Transporte de Gás - RNTG) integrates high-pressure gas pipelines (between 20 and 85 bar) and connects the gas system infrastructures - underground storage and liquefied natural gas (LNG)  terminal - and international interconnections to high-pressure consumption points (mainly power and cogeneration plants) and exits to the distribution networks. The network includes infrastructure such as pipelines and branches, gas regulating and metering stations (GRMS), custody transfer stations (CTS) and other elements.

Rules governing the use of the transmission network are defined in the Regulation on Access to Networks, Infrastructures and Interconnections (RARII), approved by ERSE, and in European Network Codes - namely the Network Code on Interoperability [Commission Regulation (EU) 2015/703, of 30 April 2015] and the Network Code on Capacity Allocation Mechanisms [Commission Regulation (EU) 2017/459 of 16 March 2017] - the implementation and monitoring of which is assigned to National Regulatory Authorities and to the European Union Agency for the Cooperation of Energy Regulators (ACER).

To find out more about this, have a look at the pedagogical guide Natural gas: how does it work?