The Sudanese assets accounted for more than half of the portfolio's 12.88 million tonnes of output in 2003, and according to Deutsche Bank, they account for 52 percent of CNPC's overseas crude reserves of 1.76 billion barrels.

"The Sudanese assets are not expected to be included," the source, who asked not to be identified, told Reuters on Wednesday.

PetroChina , the country's largest oil and gas producer, said last month it might buy multi-billion dollar overseas assets from its state-owned parent. But it did not give details.

PetroChina has few assets abroad, and its crude output is flagging in ageing oil fields. A purchase of all of CNPC's overseas assets in one hit would have boosted PetroChina's output by up to 15 percent.

Analysts have expressed concerns that an injection of CNPC's Sudan assets would increase PetroChina's risk profile.

A two-year old armed rebellion in Sudan has left 5.5 million people in need of food aid there, according to the United Nations, and the United States has been pushing for U.N. sanctions against its oil industry.

Deutsche Bank values all of CNPC's overseas reserves in countries including Sudan, Kazakhstan, Indonesia and Venezuela, at $6.2 billion.

Buying all of them would have made PetroChina, already the world's sixth largest listed oil firm by market value, into a player with large-scale hydrocarbon assets around the world, and daily oil and gas output close to 3 million barrels of oil equivalent (boe).

Before it took PetroChina public in 2000, CNPC had planned to include all of its overseas assets in the subsidiary. But it dropped the plan later due to worries that inclusion of assets like the Sudanese fields would hurt U.S. investors' interest in its stock offer if it did so.