Amnesty International has accused Nigeria's biggest petroleum producer, Shell, of inaccurately documenting oil spills in an effort to avoid paying compensation and damaging its reputation.
"Shell is being disingenuous about the devastation caused by its Niger Delta operations. This new evidence shows that Shell's claims about the oil spills cannot be trusted," said Audrey Gaughran, Amnesty's director of global issues, on Thursday.
Shell Nigeria said it "firmly rejects unsubstantiated assertions" by Amnesty, adding the group "exaggerated the impact of crude oil theft and sabotage to distract attention from operational performance".
Hundreds of leaks are reported every year in the creeks and swamplands of the Niger Delta. These spills damage the environment and cut profits for oil companies, including Shell and Italy's Eni.
Sabotage and theft
Shell says most of its oil spills are caused by sabotage and theft and that it cleans up, whatever the cause.
Amnesty, however, said it saw reports about spills that stated the reason as sabotage, but lacked further explanation. Other examples showed that Shell had calculated the size of a spill behind closed doors.
Amnesty also worked with US pipeline specialist Accufacts, which found some pictures on Shell's website showing that spills categorised as being caused by sabotage were more likely due to corrosion of ageing pipelines.
Accufacts also questioned Shell's methodology in calculating the cause and size of spills.
Shell said that since 2011 it has published spill investigations with photographs on its website, and is the only oil major operating in Nigeria to do so.
"We seek to bring greater transparency and independent oversight to the issue of oil spills, and will continue to find ways to enhance this," the company statement said.
Amnesty acknowledged that Shell had improved its transparency over oil spills since 2011.