As part of its effort, the firm confirmed it has received interest from investors, including CVC. The sale is part of the firm’s effort to reduce its debt by selling non-strategic assets through 2020.

In a filing to the country's stock exchange, Repsol said: "We announce that within the 2016-2020 Strategic Plan, and as part of its permanent and dynamic business portfolio management, Repsol analyses different alternatives including those relating to its participation in Gas Natural SDG, S.A.

"In this regard, various investors, including CVC, have communicated to Repsol their interest in exploring the possibilities of its divesting its 20% stake in Gas Natural SDG, S.A."

The firm, however, said no decision has been made regarding the stake sale in Gas Natural.

In 2015, Repsol announced its plans to offload $7.1bn of non-strategic as part of a restructuring plan. The plan also included broader integration of refining and marketing activity and a clear goal of reducing energy costs and CO2 emissions.

In 2016, Repsol and Criteria Caixa, which owns Caixabank which holds 24% stake of Repsol, agreed to divest 10% stake each in Gas Natural to Global Infrastructure Partners for nearly €3.8bn.

The acquirer was GPI’s fund, Global Infrastructure Partners II I, and a group of its Limited Partner Co – Investors.

Repsol earlier said that, through ambitious efficiency program, it expects to achieve €2.1bn of savings and in operational synergies every year from 2018.

Energy infrastructure company, Gas Natural operates across the gas value chain from procurement to liquefaction, storage, regasification, transportation, distribution and marketing.

The firm also owns and operates gas distribution networks in in Brazil, Chile, Colombia and Mexico as well as electricity distribution market shares in Chile and Panama. It owns approximately 15GW of electricity generation assets.

Image: Reposol headquarters in Madrid, Spain. Photo: courtesy of Luis García (Zaqarbal)/Wikipedia.