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.

"(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. Repsol did not immediately respond to a request seeking comment. - Reuters