Royal Dutch Shell's operation in Nigeria is working to plug a leak caused by sabotage that shut its 70,000 barrel-per-day (bpd) Nembe Creek pipeline, the company said in a statement emailed to Reuters on Wednesday.
The pipeline in the swampy creeks of the Niger Delta was shut down on December 24 but went unreported, eclipsed by a much bigger leak at Shell's offshore Bongo facility.
A loading accident at Shell's offshore 200,000 bpd Bonga oilfield on December 20 spewed up to 40,000 barrels of oil into the sea and shut off some 10 percent of Nigeria's crude output.
Nigerian villagers say oil is still washing up on the coast, though Shell denies this.
The statement about the Nembe Creek spill said a joint investigation with the Bayelsa State Ministry of Environment showed oil thieves had installed valves on the pipeline. More than 200 barrels of spilled oil have been recovered, it said.
Shell blames oil theft, or "bunkering", for most of the environmentally destructive oil spills that hemorrhage from its equipment in the Delta. Human rights groups such as Amnesty International blame the firm's negligence.
Diplomats say between 100,000 and 250,000 barrels of oil are stolen each day, often with the complicity of local officials, an activity worth hundreds of millions of dollars.