Lagos - Shell Nigeria is declaring "force majeure" on exports from its Forcados crude oil terminal that stopped operating on March 4 because of a leak in its undersea pipeline.
A statement blames thieves for the leak eight meters (26 feet) underwater in the Gulf of Guinea.
The announcement of "superior force" effective from 9 a.m. (0800 GMT) Tuesday gives Nigeria's biggest oil producer some legal protection against contractual obligations.
Shell did not say how much oil has not been exported because of the alleged sabotage. Forcados can handle 400,000 barrels of crude daily, more than a fifth of the 2.2 billion barrels produced in Nigeria.
The government says it loses about 200,000 barrels daily to oil thefts that had been limited to hacking into pipelines on land in the southern Niger Delta.