LONDON— Royal Dutch Shell PLC on Wednesday said its exports of Nigerian crude oil had been significantly disrupted, adding to a slew of stoppages that have knocked out around 500,000 barrels a day of oil output in the West African country.
It is the latest hit to oil exports across the world, leading to mounting concerns about the global crude supply. A series of output interruptions from Canada to Libya have illustrated how quickly the global glut of oil could be cleared out after nearly two years of weighing on prices.
Canadian outages caused by rampant wildfires, supply disruptions caused by political disagreements in Libya and the Nigerian stoppages now add up to 3.5 million barrels of offline oil a day, said Seth Kleinman, a Citigroup analyst.
“The growing level of supply disruptions should tighten near-term balances,” Mr. Kleinman wrote in a note.
Global oil production still outpaces demand by more than 1 million barrels on any given day, weighing down crude prices that fell to their lowest levels in 13 years in 2016. Oil-market experts, including Saudi Arabia, believe supply and demand won’t balance more permanently until the end of 2016.
Oil prices were up on Wednesday as new data showed U.S. oil stock inventories had been drawn down.
Nigeria’s oil production looks particularly vulnerable amid an alarming increase in militant attacks on infrastructure in the country’s oil-rich south. Though it remains unclear what caused the latest outage, it follows a series of attacks that knocked out a significant volume of production since the start of the year.
In an emailed statement, Shell’s Nigerian subsidiary said it had declared force majeure as of Tuesday, a move that gives it legal indemnity for being unable to fulfill its export obligations. The company said a leak had closed the Nembe Creek Trunk line which pipes crude through the Niger Delta to Shell’s export terminal. The disruption will affect about 200,000 barrels a day of crude exports this month, according to a trader familiar with Nigeria’s export program.
Shell didn’t comment on the cause of the leak or the size of any associated spill. The Anglo-Dutch oil major sold the pipeline to Nigerian energy company Aiteo last year as part of a series of divestments from the restive Niger Delta, and referred further questions on the incident to the African company. Aiteo didn’t respond to a request for comment.
The incident comes a week after an attack shut down Chevron Corp. ’s Okan platform off the Nigerian coast, knocking out 35,000 barrels a day of the company’s crude output. Another of Shell’s export terminals has been out of action since February, cutting off a further 250,000 barrels a day of the country’s oil output.
Both attacks were claimed by a group calling itself the Niger Delta Avengers, which says it wants locals to have more control over the region’s oil resources and revenues.
Nigeria’s rich oil fields have a long history of militancy and criminality that frequently force oil companies to shut down production. In the 1990s, protests over oil spills forced Shell out of one part of the Niger Delta, and militant attacks last decade frequently shut down big chunks of the country’s output.
But large and sophisticated attacks on Nigeria’s oil fields seemed to die down in the wake of a 2009 government amnesty for militants. That truce may be coming to an end, with severe implications for Nigeria’s oil output.
Last month, the International Energy Agency said supply from Nigeria fell to 1.7 million barrels a day in March—its lowest level since the middle of 2009. That was before the latest set of disruptions hit.
The Niger Delta Avengers has threatened fresh attacks and said it would target international oil companies. Earlier this week, Shell evacuated nonessential personnel from one of its oil fields off the coast of Nigeria, though it said operations were continuing.
—Georgi Kantchev contributed to this article.