The Anglo-Dutch energy giant’s Nigerian arm said in a statement that the spills had been greater than the previously-reached total figure of 4,144 barrels.
The Shell Petroleum Company of Nigeria (SPDC) did not give a revised figure but a spokesman said the volume would not be a “key issue” in determining compensation.
Leigh Day, the law firm bringing a compensation bid for 15,000 members of Nigeria’s Bodo community, have claimed the spills could be as large as 600,000 barrels.
They say the local environment in Rivers State was devastated by the two spills, causing an “environmental catastrophe” and depriving thousands of subsistence farmers and fishermen of their livelihoods.
“From the outset, we’ve accepted responsibility for the two deeply regrettable operational spills in Bodo,” said a spokesman for SPDC.
“We want to compensate fairly and quickly those who have been genuinely affected and to clean up all areas where oil has been spilled from our facilities.”
He said that following the spills, a team involving government agencies, the SPDC and representatives from the Bodo community visited the sites and completed a joint investigation.
“They estimated that the total volume of oil spilled was in the region of 4,144 barrels,” the spokesman said.
“As part of the litigation process, we asked satellite remote sensing experts, hydrologists and specialists in mangrove ecology to assess how the Bodo waterways and mangroves were impacted and other relevant information addressing the question of the volume of these spills and the extent of the damage.
“Having reviewed their findings, we accept that the total volume of oil released as a result of the two operational spills is likely to have exceeded the joint investigation visit estimates.”
Leigh Day said they were due to start mediation talks with Shell on December 8.
If an agreement cannot be reached, the parties will go to a three-month High Court trial, as scheduled, in May 2015.
“After two failed attempts to negotiate a deal we are more hopeful that with the trial looming, this will be the spur for Shell to pay a fair and reasonable amount to the villagers whose lives have been blighted by these oil spills,” said senior partner Martyn Day.
“However, our clients are certainly not counting their chickens and we are ensuring that the case is ready to go to trial… if the talks fail.”
Nigeria is Africa’s biggest crude producer, but much of the Niger Delta oil region remains deeply impoverished.
Decades of spills have caused widespread pollution in the region.