and Criteria Caixa are in talks to sell up to 20 per cent of utility , a transaction that would mark another step towards disentangling the complex web of that have long marked Spain’s corporate scene.

In a statement to Spain’s stock market regulator on Thursday, Repsol said the two groups were looking to sell 10 per cent each, but cautioned that talks were at a “preliminary stage” and that no decision had been taken. Criteria, which owns a controlling stake in along with industrial stakes in Spain and abroad, issued a similarly-worded statement.

Based on Gas Natural’s current market value, a 20 per cent stake would be worth about €4bn.

The regulatory statements made no mention of the interested parties, but according to people familiar with the talks they include US funds Global Infrastructure Partners and KKR.

News of the sales talks was first reported by Bloomberg.

Repsol controls 30 per cent of , while Criteria owns 34 per cent. Criteria is also the dominant shareholder in Caixabank, Spain’s third-biggest financial group by market value, which in turn owns 12 per cent of Repsol. Even a sale of 20 per cent of Gas Natural would leave Criteria and Repsol as the most powerful voices on the board of the utility.

The sale, if it goes ahead, would form part of a broader portfolio realignment both at Repsol and Caixa. Like other oil and gas groups, by the recent sharp fall in oil prices, made worse still by the group’s ill-timed acquisition of a Canadian energy company. In an attempt to shore up its balance sheet, Repsol has already sold assets worth €2.8bn over the past year, including wind farms in the UK and piped gas business in Spain.

The Caixa group, meanwhile, has been working to streamline its sprawling portfolio and create a clearer separation between its banking arm, Caixabank, and its industrial holding. Among other steps, it announced this year a plan to sell down its from the current 56.8 per cent to no more than 40 per cent.