The crude oil grade, Nigeria's largest export stream, has been under force majeure since mid-July, when the company said it detected a "system anomaly" on the line.

Sources said the company later found substantial damage to the subsea line that would take at least one to two months to repair.

An Exxon spokesman declined to comment on the plan to use an alternative pipeline, saying: "We're continuing to make progress, but we would not speculate on a timeline for repairs."

(Reporting by Libby George and Julia Payne; editing by Jason Neely)