Gas Natural SDG, S.A., trading as Gas Natural Fenosa (Spanish pronunciation: [ˈɡaz natuˈɾal feˈnosa]), is a Spanish natural gas and electrical energy utilities company, which operates primarily in Spain. The company's administrative headquarters are in Barcelona, while its registered office is in Madrid.

It also has operations in other countries, including: Italy, France, Germany, The Netherlands, Belgium, Mexico, Colombia, Argentina, Puerto Rico, Moldova, and Morocco.

The corporation's main interests are: the distribution of natural gas in Spain, Italy, and Latin America; the generation and commercialisation of electricity in the liberalised Spanish market (1997-2009); and the management of natural gas infrastructure and shipping transport.

Gas Natural has approximately 10,000,000 energy clients worldwide. It has around 6,700 employees, of which approximately 50% work within Spain.

The group's largest shareholders include the Spanish La Caixa bank and Repsol global energy company.

Gas Natural acquired utility company Unión Fenosa for around €16.8 billion in 2009.

The company's administrative headquarters complex, Edifici Gas Natural or Torre Mare Nostrum, is located in the La Barceloneta neighbourhood of the Ciutat Vella district in Barcelona. Its registered office is being moved to Madrid.

The skyscraper was designed in the High-tech architectural style by the EMBT Architects firm of architects Enric Miralles and Benedetta Tagliabue, and was completed in 2005.