A landmark trial is unfolding in Ecuadorian Amazon, where a group of rainforest residents is suing Texaco for $6bn in oil clean-up costs.

Texaco, now part of Chevron, admits to dumping 18 billion gallons of run-off while drilling for oil in the rainforest, but the company says it did so legally and according to industry standards.

Environmentalists call it the worst oil-related disaster in the world – Texaco allegedly dumped 30 times the amount of crude spilled by the Exxon Valdez.

Al Jazeera's Mariana Sanchez reports that the plaintiffs say the company left hundreds of dump sites, many of them unlined, and open-air pits that ooze toxic sludge into what was once pristine rainforest.

The Cofan, an indigenous nation of less than 500 men and women, say their land is contaminated and are filing a lawsuit against the giant oil company.

"The water stunk and so did our fish. In the end, we were left there, with sadness, thinking where will we get fresh water?"

These tribesmen are demanding a clean-up. They are part of the 30,000 plaintiffs who filed a class action lawsuit in New York in 1993 and lost the case. The case is now being tried in Ecuador.

In 2001 Chevron bought Texaco, taking over its assets and this legal battle.

"Texaco created a system where they dumped literally billions of gallons of toxic waste water", said Steven Donziger, legal counsel.

Donziger, who represents the plaintiffs, says the dumping saved the company billions of dollars in operating costs.

"When you do this every day with 300 well sites in 28 years you have an ecological disaster and that’s what we are looking out today," he said.

Meanwhile, Ricardo Reis Vega, Chevron’s legal counsel and vice president, argues the company cleaned up the areas under Chevron’s obligation.

"The part that was in our responsibility inside the scope of work was done 100 percent," Vega said.

In 1995 the Ecuadorian government agreed to release the company from further responsibilities after they cleaned up.

The Amazon Defence Front, also representing the 30,000 plaintiffs, says most of the damage has been left untouched. And the pollution, they say, is not biodegradable.

"This is how Texaco designed their pits and they are still working today. The pollutants come from a pool through a tube into the swamp and the swamp feeds the river from which the Cofan take their water."

The American company says it spent $40m on remediation but that is only one per cent of the amount the Cofan's lawyers estimate is needed for a real clean up.