Amnesty International has accused major oil companies, including Shell, of failing to report the true picture of oil spills in Nigeria.
Amnesty says oil companies often blame oil spills on sabotage in order to get out of paying compensation when in fact corroded pipes are the cause.
The report says the process of cleaning up the oil spills is completely discredited.
Shell said it "firmly rejects unsubstantiated assertions".
It highlighted the issue of theft of crude oil, which it said "remains the main cause of oil pollution in the Delta".
Oil spills are having an appalling environmental impact on the Niger Delta and they are happening at an alarming rate, says the BBC's Will Ross in Lagos.