Chevron is one of the west African country's top producers and typically loads two 920,000 barrel tankers a month from its Kuito platform.

"The Kuito operation is currently undergoing a planned turnaround, and we do not anticipate any resulting production impacts from this action," a company spokesman said in an emailed statement.

Angolan loading programs showed that Chevron was due to load just one 920,000 barrel tanker in November, reflecting the impact of the maintenance work.

Trade sources said that the force majeure was declared because of technical problems with mooring equipment at the Kuito site, located about 30 miles offshore. A force majeure allows a company to suspend contractual obligations in the face of unexpected events.

OPEC member Angola is Africa's second largest producer after Nigeria and typically exports around 1.8 million barrels per day (bpd) of crude oil.

Exports for November are slightly lower than average at around 1.67 million bpd, partly due to lower Kuito output and lower volumes on the Girassol grade.

(Reporting by Emma Farge; Additional reporting by Jonathan Saul in London, editing by William Hardy)

• A Permanent Economic Emergency