China's CNOOC is exploring a potential $15 billion joint venture with Repsol, involving the Spanish oil company's global exploration and production assets, a source familiar with the matter said.

CNOOC's pursuit of a Repsol joint venture would include the Chinese company's existing plan to purchase 25 percent of Repsol's YPF oil business in Argentina, the source said.

State-owned Chinese energy giant CNPC is also trying to buy a stake in YPF.

Repsol spokesman Kristian Rix denied that the company was considering a joint venture with CNOOC.

But the source familiar with the matter said CNOOC's plans included Repsol assets beyond Argentina.

(CNOOC) is interested in something more than YPF, the source told Reuters.

CNOOC, China's top offshore oil group, is exploring a partnership with Repsol involving upstream E and P assets in its global portfolio, the source said, adding that such a deal could be worth roughly $15 billion.

Goldman Sachs, the bank advising Repsol on the sale of YPF, and CNOOC declined to comment.

The source, who has direct knowledge of the deal, was not authorised to speak publicly about the process and so wished to remain anonymous.

CNPC, parent company of top Asian oil and gas company PetroChina, has been in talks to buy 75 percent of YPF, sources have previously told Reuters.

Sources have said CNOOC is eyeing a 25 percent in YPF.

Chinese state oil companies have been involved in a string of takeovers to satisfy China's need for energy supplies to fuel a fast-growing economy.

(Reporting by Joseph Chaney, editing by Will Waterman)