China's buying of West African crude oil is set to rise about 15 percent in September from August, trade sources said on Friday, but overall Asian imports from West Africa will fall due to slower Indian demand.

Meanwhile, U.S. companies have resumed buying light sweet crude after having suspended spot purchases following the release of oil from the Strategic Petroleum Reserve, the sources said.

Chinese imports of oil from producers such as Angola and Nigeria are estimated to average 918,000 barrels per day (bpd) in September, the largest volume since March. The August imports are expected to total 797,000 bpd.

Unipec, the oil trading arm of Sinopec Corp, appeared as the biggest corporate buyer of West African crude, buying at least 633,000 bpd for September loading, mostly Angolan crude. More than a quarter of Angolan crude was sold to Unipec.

ConocoPhillips followed Unipec as the second-largest corporate buyer. It bought about 10 cargoes, or about 320,000 bpd, in September, mostly Nigerian sweet crude.

ConocoPhillips scooped up the cargoes towards the end of the trading month of September, while it bought nearly no West African crude for August loading as it procured sweet crude from the SPR as a part of the emergency oil stock release coordinated by the International Energy Agency in late-June.

The September market turned to be strong, a physical oil trader said.

Conoco's move definitely supported the market and Angolan cargoes were sold very quickly to Chinese buyers.

The increase in U.S. demand pushed up spot differential on Nigerian light, sweet benchmark Bonny Light and Qua Iboe to about dated BFOE plus $2.90/$3.00 a barrel, recovering to the May level before the announcement of the SPR release.

The differentials on Nigerian light sweet crude had fallen to dated plus $1.60/$1.70 in July because of the release, which was meant to fill in the loss of oil exports from war-torn Libya.

The Chinese and U.S. demand offset the fall in Indian demand for West African crude. The volume will halve to about 253,000 bpd in September from 523,000 bpd in August, lowering total Asian imports.

Total Asian imports of West African crude will average 1.39 million bpd in September, compared with 1.59 million bpd in August.