The Argentine unit of Brazilian state-controlled oil giant Petrobras said Monday that it discovered unconventional petroleum in Argentina's Vaca Muerta formation.

"The discovery occurred during the post-stimulation test drilling at well RDA.x.1001," Petrobras Argentina said in a filing with the Buenos Aires stock exchange.

The well is part of the Rincon de Aranda concession in Neuquen province, operated by Petrobras Argentina in a 55 percent/45 percent partnership with French oil major Total.

"It is not yet possible to estimate the reserves associated with this discovery, which will require additional studies and drilling," Petrobras Argentina said.

The oil was detected at a depth of 2,501 meters (8,200 ft) below the surface.

Vaca Muerta, which encompasses a total of 30,000 sq. kilometers (11,500 sq. miles) in west-central Argentina, is one of the world's largest shale oil and gas fields. EFE