* U.S. fund GIP in preliminary talks to buy stake -sources
* Twenty pct stake has market value of around $4.2 billion
* Gas Natural shares close up 3.05 pct at 19.07 euros (Adds details on Gas Natural stake, GIP)
By Andrés González
MADRID, Sept 1 (Reuters) - Spanish oil firm Repsol and Criteria Caixa, an industrial holding company that owns Caixabank, said on Thursday they were in talks with various investors to each sell around 10 percent of Gas Natural .
Two sources familiar with the matter told Reuters earlier that U.S. investment fund Global Infrastructure Partners (GIP) was in preliminary discussions with Repsol and Criteria to buy part of Gas Natural.
Repsol and Criteria did not confirm which investors they were talking to. However, they said in separate statements to the stock market regulator that they were exploring the sale of a combined 20 percent in the Spanish gas company.
A 20 percent stake of Gas Natural has a current market value of around 3.8 billion euros ($4.2 billion).
GIP, whose executives are former Credit Suisse and General Electric employees, is already present in Spain through a 24 percent stake in the renewable energy group Saeta Yield.
The New York-based investment fund said it would not comment on speculation or market rumours, while Gas Natural declined to comment.
“Repsol and Criteria are in contact with various investors,” Repsol said in a filing to Spain’s stock market regulator. “This analysis is in a preliminary phase, and no decision has yet been taken.”
Criteria - the holding company of Caixabank and which has stakes in other Spanish companies such as infrastructure group Abertis - holds 34 percent of Gas Natural while Repsol has 30 percent in the company.
Criteria values its Gas Natural stake at 16.2 euros per share on its books, while Repsol values its own stake at 15.8 euros. Shares in Gas Natural closed 3.05 percent up at 19.07 euros.
Repsol has sold off various assets in recent months, such as an offshore wind power business in Britain, as it looks to trim its debt.
Criteria and its banking unit, meanwhile, are both under pressure to boost their solvency ratios in a more demanding global regulatory environment.
In last month’s Europe-wide stress test, both Criteria and Caixabank were among the weakest links in the health checks.
Bloomberg earlier reported the sale could value the Gas Natural stake at about 4 billion euros, citing sources familiar with the matter.
Analysts at Banco Sabadell said this price tag would be positive for the gas company, though they added this initial stake sell-down raised the possibility of further disposals, which could weigh on the shares.
“This disinvestment would be the official declaration by Repsol and Criteria that their remaining stakes (in Gas Natural) are not strategic for either of them,” the analysts said. (Additional reporting By Jesús Aguado; Writing by Sarah White; Editing by Adrian Croft and Mark Potter)