A court in Ecuador has fined Chevron a reported $US8 billion for polluting a large part of the Amazon region.
Texaco, which merged with Chevron in 2001, was accused of dumping more than 18 billion gallons (68 billion litres) of toxic materials into unlined pits and Amazon rivers between 1972 - 1992.
Campaigners say crops were damaged and farm animals killed and that local cancer rates increased as a result.
Chevron says it will appeal the decision. A statement described the ruling as "the product of fraud (and) contrary to the legitimate scientific evidence".
Asked by BBC News if the fine imposed did indeed amount to $US8 billion, Chevron said it was still not clear. It said it was still "trying to decipher" the ruling.
The lawsuit was brought on behalf of 30,000 people, in a case which has dragged on for nearly two decades.
The BBC reports the trial began in 2003 after almost a decade of legal battles in the United States. At that time, a US appeals court ruled that the case should be heard in Ecuador.
Environmentalists hope the case will set a precedent.