UPDATE 3-CNPC eyes $14.5 bln bid for Repsol YPF stake-sources

* CNPC could pay $14.5 bln for 75 pct of Repsol unit

* CNPC, Repsol executives in talks, sources say

* Joint bid by CNPC, CNOOC possible, analysts say

* Repsol shares lag oils sector

(Adds analyst quotes, background)

By Joseph Chaney and Sui-Lee Wee

HONG KONG/LONDON, July 7 (Reuters) - China National Petroleum Corp. (CNPC), the country's largest oil company, could pay up to $14.5 billion for 75 percent of Spanish oil major Repsol's (REP.MC) Argentine unit YPF, sources said on Tuesday.

CNPC, parent company of top Asian oil and gas firm PetroChina (0857.HK) (PTR.N) (601857.SS), and Repsol have begun talks, sources with knowledge of the matter told Reuters.

The sources, not authorised to speak publicly, said an offer from CNPC -- which in 2007 failed twice to buy all of YPF's Latin American assets amid wrangling over terms -- had yet to be put on paper or formally submitted.

China's top offshore oil and gas producer CNOOC (0883.HK) (CEO.N), India's Oil and Natural Gas Corporation (ONGC.BO) and Russian companies are also eyeing YPF, newspaper reports said.

Repsol, ONGC, and CNOOC all declined to comment, and a CNPC spokesman said he had no information the deal.

Last week Repsol, which is running short of reserves but has been looking to sell YPF for some time, said it had several offers for a stake in the unit, but none were firm.

Analysts have valued YFP at around $15-17 bln so the around $19 bln implied by the bid CNPC is mulling would offer shareholders only a modest premium.

At 1000 GMT, Repsol was trading up 0.6 percent at 16.39 euros, underperforming a 2.8 percent gain for the European oil and gas sector .SXEP.

"We don't believe there is likely to be significant value upside from a deal unless it implies a value well over $17 billion," Gordon Gray , oil analyst at Collins Stewart, said last week.

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