CNOOC, China's third biggest oil and gas group, is considering a bid of more than $13 billion (€9.8 billion) for its US rival Unocal in a deal that would mark the largest and most significant overseas acquisition by a Chinese company.

Sources close to the state-controlled group said it was interested in Unocal's assets in Indonesia, Thailand, Bangladesh and Burma and had asked bankers to study a takeover of the company.

However, the negotiations were said to be at an early stage and CNOOC is also looking at other overseas targets.

CNOOC's plans are the latest sign of Beijing's determination to push its flagship companies to acquire natural resources to fuel the country's economic growth.

CNOOC is the latest Chinese company to appear on the global acquisitions stage. Last month Lenovo, the computer maker, bought IBM's personal computer business for $1.75 billion, while state-owned Minmetals failed to buy Noranda, the Canadian mining giant.

Industry experts said buying Unocal, which is valued at $11 billion, would be difficult for CNOOC, whose market value is about $21.5 billion.

However, the Chinese company would be able to draw on financial help from its state-owned parent company, China National Oil Offshore Corporation .