UPDATE 1-CNOOC in talks to join CNPC in YPF bid -source

* In talks to join in $14.5 bln bid for Repsol's YPF-source

* Potential joint bid would see CNOOC get 25 pct of YPF (Adds details, background, analyst quote)

By Joseph Chaney

HONG KONG, July 10 (Reuters) - China's top offshore oil and gas producer CNOOC (0883.HK) is in discussions to support China National Petroleum Corp's (CNPC) expected $14.5 billion bid for Spanish oil major Repsol's (REP.MC) Argentine unit YPF, a source with direct knowledge of the matter said.

CNPC, parent company of top Asian oil and gas company PetroChina (0857.HK) (PTR.N) (601857.SS), is in talks to buy 75 percent of YPF, sources said earlier this week.

CNOOC (CEO.N) is now in discussions to launch a joint bid with CNPC and is eyeing 25 percent of YPF, a source told Reuters on Friday.

The source was not authorised to speak publicly about the matter and declined to be identified.

"All the parties involved are in discussion for a joint bid," the source said, adding that the process is at an early stage.

A CNOOC spokesman was not immediately available for comment.