Oil firm Royal Dutch Shell was told a pipeline had reached the end of its life years before it spilled up to 500,000 barrels of oil, according to court documents seen by the BBC.
Two spills in 2008 affected about 35 sq miles (90 sq km) in southern Nigeria, according to a group suing Shell.
The area included sensitive mangroves.
Shell “dismisses the suggestion that it has knowingly continued to use a pipeline that is not safe to operate,” it told the BBC.
The emails, letters and internal reports submitted to a court in London show that senior Shell employees were concerned before the spill that Shell’s pipelines in the area had reached the end of their lives and needed replacing to avoid danger to lives, the environment and the economy.
The spills took place in Bodo, a town in the Ogoniland region, where people interviewed for an Amnesty International report into the effects of the incident reported headaches and eyesight problems.
Following the spills, the price of fish, a local staple food, rose as much as tenfold, according to Amnesty. People who worked in fishing had to find jobs in other industries which proved more difficult to find.
Oil spills in the Ogoniland region have also contaminated local drinking water sources, seeping into groundwater, according to a report from the United Nations Environment Programme (UNEP). Toxins found by UNEP in the wider Ogoniland area’s drinking water include benzene, which is thought to cause cancer.
The two spills came from the same pipe on the Trans Niger Pipeline, operated by Shell, which takes oil from its fields to the export terminal at Bonny on the coast. It carries about 180,000 barrels of oil per day. The firm disputes the size of the spills and says much of the oil was spilt as a result of thefts and sabotage.
In September 2006 – two years before the spills – a letter from Basil Omiyi, managing director of Shell’s Nigeria business, SPDC, to the governor of Rivers State said that the pipeline was of “immediate and utmost concern”.
Shell had not inspected the pipeline for several years due to difficulties in accessing it, he said.
“There is a risk and likelihood of rupture on this pipeline at any time, which if it happens, could have serious consequences for the safety of life, the environment and the nation’s economy.”