A faded sign welcomes visitors to "Lago Agrio, living earth". The town of 103,000, on the border of Colombia and Ecuador, is now at the centre of the biggest environmental lawsuit in history, with $27bn in potential damages.

The main street of Lago Agrio today. The town was founded in virgin Amazon jungle in the early 1960s as the base camp of a Texaco Petroleum-Gulf Oil exploration project that by 1974 had become a joint Texaco-PetroEcuador consortium. Texaco, with a 37.5 per cent stake in the business, was the operator, while the state-owned oil company held a 62.5 per cent interest.

A resident with newly-installed water tanks provided by Unicef and local NGOs which is their only source of clean water.

Sewage flows directly into a stream on the outskirts of Lago Agrio. Locals complain of constant water rashes and stomach upsets that plaintiffs in the case attribute to the release of 18bn gallons of produced water - the hot, very salty by-product of drilling that can also contain chemicals - directly into waterways during the Texaco years, and oil pollution of groundwater. Chevron says a lack of sewage management and water treatment plants have led to bacterial contamination of water.

Shushufindi-61, an unremediated pit that dates back to the Texaco-PetroEcuador consortium. Chevron argues the pit was not included in its 1995 clean-up agreement with the Ecuadorean government and was thus the responsibility of PetroEcuador. The plaintiffs dispute the validity of the 1995 agreement, and the quality of remediation the company carried out.

James Craig, spokesman for Chevron, stands on the site of an oil pit remediated by Texaco as part of a 1995 agreement with Ecuador's government to clean up 37.5 per cent of the well sites at a cost of $40m to end its part in the consortium. Chevron says its release, signed by the government, absolves it of further responsibility in the clean-up of the region. The plaintiffs say the government had no power to authorise such a release, and dispute the quality of Texaco's remediation work.

A schoolgirl crosses a bridge surrounded by oil pipes between Shushufindi, another major oil field near Lago Agrio.

A deactivated pump in a residential area outside of Lago Agrio. When Texaco began operations in the early 1960s, the government decided to open up the area for colonisation. Today the population is a mix of migrants from other parts of Ecuador, indigenous peoples and Colombian refugees.

A local resident whose parents' house sits beside an unremediated oil well site.

Patients in the local health clinic. Leonor Velasquez, far right, blames Texaco for the rashes and illnesses many residents suffer. "All of the water we have to drink or bathe in is contaminated," she says.

Donald Moncayo, a local environmental activist who runs "toxic tours" of the old oil pits, digs into the side of the creek bed behind an abandoned house to reveal heavily polluted soil. Chevron argues that much of the pollution in the region today is the responsibility of PetroEcuador, which still operates here; the plaintiffs maintain that Texaco, although a minority partner in the consortium, was the operator and therefore responsible for the full environmental impact of its work in the region.

Roberto and Anita-Ruíz Ponce and family; the Ponce's son José Luis died of leukaemia the day after his 17th birthday. The Ponces believe their son's illness was caused by contamination from the oil industry.

About 30 paces from his family home, Mr Ponce watches as Donald Moncayo digs down to an old remediated pit to find oil mixed with soil.

A handful of soil from the pit near the Ponce's home.

Mr Ponce removes the cover from the family well that they now believe is tainted. A court-appointed expert found an elevated incidence of cancer in the region. Chevron accuses the court and the expert of bias, and says no evidence has been presented.

A pipeline runs down the main street of Shushufindi, where most locals rely on the industry for work.

An unremediated oil pit in the jungle dating back to the Texaco-PetroEcuador concession. The locals call the pits piscinas, or swimming pools, and below the semi-hard crust of this pit there is a thick black liquid crude mix.

Donald Moncayo tests the depth of the pit with a pole more than 2m in length.

Oil from the pit drips off a pole.

PetroEcuador's headquarters.