Under the preliminary agreement, the companies would jointly develop a 187-square-kilometer (72-square-mile) swath of Vaca Muerta in the southern Patagonia region, YPF said in a statement.
YPF, which was nationalized in 2012 through a seizure of Repsol's majority stake in the company, has been seeking international partners to help it develop Vaca Muerta.
Vaca Muerta is considered one of the world's biggest known deposits of unconventional energy, with 661 billion barrels of oil and 1,181 trillion cubic feet of natural gas resources, according to YPF.
(Reporting by Alejandro Lifschitz; Editing by Lisa Von Ahn)