The liberalisation process of the natural gas sector of most European countries was carried out in stages, starting by the customers of higher annual consumption.

In Portugal, a similar methodology was followed, and the market opening took place gradually between 2007 and 2010, initially applying to electricity producers under the ordinary regime and finally to all customers. Since January 2010, all consumers in mainland Portugal can choose their natural gas supplier.

Portugal has no natural gas resources of its own. The supply of natural gas to the Portuguese market is carried out through long term take-or-pay contracts where the main suppliers are Algeria and Nigeria.

The organisation of the Portuguese Natural Gas System (SNGN) is fundamentally based on the exploitation of the public network which is formed by the National Transmission Network, the Underground Storage Facilities, the LNG Terminal and the National Distribution Network.

The supply of natural gas is subject to public service obligations which is the responsibility of all operators in the natural gas sector including:

• safety, continuously and quality of supply
• ensuring that the service provided is universal
• ensuring the connection of all clients to the networks
• protection of customers namely in terms of tariffs and prices

The following rights are guaranteed to the agents and consumers of this sector:

• freedom of access to the exercising of the activities
• no discrimination
• equal treatment and opportunities
• impartiality of decisions
• transparency and objectivity in rules and decisions
• access to information and the safeguarding of the confidentiality of commercial sensitive information
• freedom to choose their natural gas supplier.

The main activities of the Natural Gas System can be described as follows:

• Acquisition/Import: Natural gas is extracted from underground deposits and reaches Portugal mainland through gas pipelines (in gaseous state) or aboard LNG carriers that unload at the Sines Terminal (in liquid state – LNG).
• Reception, Storage and Re-gasification: these activities take place at the Sines terminal, the only one in the country, which began operations in 2004. After the liquid natural gas is unloaded from the LNG carriers, it is stored in tanks and later re-gasified according to the country's consumption needs. There is also a quantity of natural gas which is not re-gasified and which is transported by tankers to autonomous gas units.
• Underground Storage: this activity is mainly to ensure country's safety reserves, essential to promote conditions to guarantee the supply of natural gas to the country. In addition to the safety reserve, there is also an operational reserve which allows the management of a stock of natural gas to guarantee the availability of this product if there is a need for additional supply.
• Transmission: allows the transport of natural gas in gaseous state, through High Pressure networks (higher to 20 bar) for reception and delivery to distributors, suppliers or large customers The transmission activity also includes the transport of liquefied natural gas in tankers to the autonomous gas units and respective delivery to distributors or large customers.
• Distribution: allows the distribution of natural gas in gaseous state, through Medium and Low Pressure networks (less than 20 bar) for reception and delivery to end users. The distribution activity also includes the reception, storage and re-gasification of natural gas in autonomous gas units and its delivery to supply points through the respective distribution networks.
• Supply: gas suppliers are responsible for managing the relations with the end customers, including billing and energy-related advice and support. In Portugal mainland, the supply of natural gas can be done with suppliers on the liberalised market and under specific circumstances on the regulated market with the supplier of last resort.

The following activities are subject to regulation: reception, storage and LNG re-gasification, underground storage, transmission, distribution and natural gas supply as well as logistic operations for the switch of supplier.