UPDATE 1-Argentine YPF, Bridas in shale investment deal -sources

BUENOS AIRES, Dec 28 (Reuters) - Argentina's state-controlled energy company YPF has reached a deal for Bridas Holding to invest in the country's vast Vaca Muerta shale resources, two industry sources said on Friday.

Bridas Holding's owner Carlos Bulgheroni, an Argentine oil mogul, told Reuters earlier this month his company was considering making a substantial investment in partnership with YPF. A day later, YPF's CEO said he hoped to finalize the farm-in arrangement before the end of the year.

No one in Bridas could immediately be reached to comment, and a YPF spokesman declined to comment. YPF has called a news conference for 5:30 p.m. local time (2030 GMT).

YPF says it needs to invest over $30 billion in the next five years, $4.5 billion of which is to come from strategic partners, to help pay to develop Argentina's shale oil and gas resources.

Finalizing a deal with Bridas would be the first major investment accord signed by YPF since May, when Argentina's left-leaning government seized a majority stake in the company from Spanish oil firm Repsol.

YPF signed a letter of intent for a pilot partnership with U.S. oil major Chevron Corp on Dec. 19 that aims to pave the way for major future investment in shale oil resources.

In 2010, YPF announced the discovery of the mammoth Vaca Muerta ("Dead Cow") formation in southern Argentina, which contains an estimated 23 billion barrels of oil equivalent.

Bridas Corp, half owned by Bridas Holding and half by China's CNOOC, holds 40 percent of Argentina's Pan American Energy. The remaining 60 percent is held by BP.