By Eliana Raszewski

BUENOS AIRES Argentina's President-elect Javier Milei selected a senior energy executive to lead state oil company YPF on Wednesday, his spokesperson announced, in one of the leader's first major economic decisions after his triumph at the polls last weekend.

Horacio Marin heads exploration and production for Tecpetrol, which runs the Fortin de Piedra oil and gas field within Argentina's prolific Vaca Muerta shale formation, one of the world's largest.

Milei's press team distributed a photo of Marin on Wednesday, seated at a table along with other members of the transition team.

YPF is one of Argentina's top domestic sellers of refined fuels, and also leads development of Vaca Muerta, a key supplier of natural gas and crude oil.

Milei, a far-right libertarian, won last Sunday's run-off presidential election, and will take office on December 10. During the campaign he vowed to privatize state-controlled companies like YPF, but stressed that such entities would need to gain value first.

YPF shares traded in New York are up nearly 40% since Monday, while the company's shares listed in Buenos Aires have gained nearly 55% since Tuesday.

The Argentine government holds 51% of YPF shares.

Marin was a key force behind the successful development of the Fortin de Piedra and El Tordillo fields, according to a source who requested anonymity to speak candidly about the pick.

Tecpetrol, which produces oil and gas in countries including Argentina, Mexico and Colombia, is a unit of Luxembourg-based Techint, the parent of steelmakers Tenaris and Ternium.

YPF was seized by the Argentine government of then-President Cristina Fernandez de Kirchner from Spain's Repsol in 2012.

Milei's libertarian, pro-privatization policies are in sharp contrast to the statist ones of leftist Fernandez de Kirchner, who is the country's outgoing vice president.

(Reporting by Eliana Raszewski; Additional reporting by Rodrigo Campos; Writing by David Alire Garcia; Editing by Christian Plumb and Alistair Bell)