Natural gas was introduced in Portugal in 1989 with the publication of Decree-Law No. 374/89, October 25, which defined the import regime, storage and processing and distribution of natural gas. Portugal started to be able to increase the competitiveness of its industry, particularly the more energy-intensive, to facilitate social development and the well-being of populations and to improve the security of energy supply.

The organization of the National Natural Gas System (SNGN) based on the operation of the public natural gas network, constituted by:

• National Transport Network.
• Storage and Terminal Facilities.
• National network of natural gas distribution..

The exploitation of these infrastructure is achieved through public service concessions or, in the case of local autonomous distribution networks, through public service licenses.
Gas Autonomous Unit (GSU)
The installation of high-pressure pipelines (final installation network) does not appear economically viable in certain regions of Portugal. To overcome this lack of profitability in the construction of the natural gas system were created UAG's in various parts of the country.
The autonomous units of gas are structures with low LNG storage capacity (between 80 and 160 cubic meters), supplied through tankers, usually from the port of Sines.

Currently, the national natural gas distribution network (at lower pressures) can be broken down for six concession areas and seven autonomous distribution networks.
It is noteworthy that all the elaborate designs, such as gas installations, networks Gas Secondary, Reservoirs and Registrations must meet the requirements set by the utility company in the region where the project falls.
Regional Natural Gas Distribution - Awards

• EDPGás - Portgas: North Coast Region (Porto districts, Braga and Viana do Castelo)
• Lisboagás: District of Lisbon
• Lusitaniagás: Region Central Coast (districts of Aveiro, Coimbra and Leiria)
• Setgás: Setúbal
• PeninsulaTagusgás: Vale do Tejo Region (districts of Santarem and Portalegre)
• Beiragás: Interior Region Center (districts of Viseu, Guarda and Castelo Branco)

Natural Gas Regional Distribution - Distribution License
The distribution in non-concession areas (Algarve, Alentejo and Tras-os-Montes and Alto Douro) is in charge of distribution companies that acquired licenses this feature from Gas Autonomous Units (UAG).

• Tras-os-Montes and Alto Douro - Sonorgás and Duriensegás
• Alentejo - Dianagás and Paxgás
• Algarve - Medigás