China National Petroleum Corporation (CNPC), China's biggest oil and gas producer, has signed agreements with Sudan to expand a refinery and swap oil production assets. according to a statement on the company's website Friday.

The refinery, based in Khartoum, in which CNPC and Sudan each have equal stakes, would undergo a second expansion, but the statement did not give details.

The refinery was established in 1997 and began production three years later with a designed annual processing capacity of 2.5 million tonnes. It was expanded in 2006. It processes annually 5 million tonnes of oil, and supplies 80 percent of the refined oil in Sudan.

CNPC would partially swap a shareholding in Block 6 with Malaysia's Petroliam Nasional Bhd's Block 5A in Sudan, according to the statement, without giving details.

The company also announced it had signed an agreement with the Sudanese government on advance payment for crude oil supplies.

CNPC has eight oil projects in Sudan, covering areas such as geophysical prospecting, well drilling, construction, and pipelines.