By Michael Voss
BBC News, Amazon basin, Ecuador
The tribes say they are prepared to fight to protect their land (pic: Earthrights International)
One of South America's poorest countries, Ecuador, is believed to be sitting on huge untapped reserves of oil and gas.
Much of it, though, lies beneath remote areas of the Amazon rainforest.
Now the indigenous people of the region are starting to organise themselves politically in a bid to keep the oilmen out of their ancestral homes.
In global oil terms, Ecuador is a relatively small player. But revenues from its existing Amazon oil reserves are critical in keeping the country's economy afloat.
Now, with the country sitting on huge potential new reserves, there is enormous pressure to expand production.
The difficulty is that much of it lies beneath pristine virgin rainforests which are legally designated indigenous tribal territories.
In 1999 the government sold exploration rights in two areas, known as Blocks 23 and 24, which are at the heart of Indian reserves - without consulting the tribes involved.
Six years later and exploration has yet to get under way.
There are three indigenous peoples living within these Blocks: the Achuar, Shuar and Kichwa peoples. Each has set up political organisations to help keep the oilmen out of their territories.
Milton Carrera is president of the Achuar, a tribe of about 5,000 people living in one of the remotest areas of the rainforest, near the border with Peru.
Last year he travelled to the US to picket shareholder meetings.
His is a life that straddles two worlds. When we met he was dressed in neatly pressed trousers and shirt with a colourful traditional headband made of toucan feathers, his face painted with intricate designs.
"The indigenous territories are our ancestral lands," he told me.
"We were here thousands of years before Christopher Columbus arrived. The land can't be touched, it's our inalienable right."
History of destruction
One reason that there is such bitter opposition to the plans is that Ecuador's original Amazon oilfields have left a legacy of deforestation and environmental damage.
The American company Texaco first discovered oil in Ecuador 40 years ago.
Now, almost 15 years since it pulled out of the country, the company - which has become ChevronTexaco - is facing a multi-billion-dollar lawsuit there.
Indians say oil companies harm both the environment and society
The company is on trial, accused of using outdated technology which contaminated the soil and water systems, causing widespread health problems.
ChevronTexaco denies the charges, claiming that it carried out an effective clean-up programme before leaving the country.
But whatever the outcome of the case, those in the southern Amazon basin are understandably reluctant to let the oil companies in.
"We know that here in Ecuador the industry has had a significant environmental impact," said an Achuar leader, Santiago Kawarin.
"It's had a cultural impact too, creating all sorts of social problems for indigenous communities. That is why from the very beginning we have said No, we won't work with the oilmen."
The Achuar have legal title to the land but under Ecuador's constitution the state has sole right to anything beneath the soil - in other words all mineral rights.
Bill Twist is the founder of the Pachamama Alliance, which works with indigenous Amazonian groups on issues such as land rights and sustainable development, and believes the country is under enormous international pressure to maximise oil production.
"The main external pressure comes from Ecuador's foreign debt," Mr Twist said.
"It is completely indebted, has no chance of paying it off and is under tremendous pressure from the International Monetary Fund to continue to expand the oil frontier into the Amazon region."
Oil sales account for about a quarter of GDP and according to the former Minister of Energy Rene Ortiz, who is now president of the country's Petroleum Industry Association, the oil revenues go towards paying for both state sector salaries and a significant amount of the national debt.
He fears that with Ecuador's oil sector has been gridlocked by the Texaco trial and the Indian opposition.
"The oil sector is paralysed because the government has been unable to put together a bidding round for the last 10 years or sign any new contracts for exploration and production for the past five years," Mr Ortiz said.
Now there are fears that the conflict could become militarised.
Already there have been clashes with the army in Kichwa territory, while in a separate incident, a group of oil exploration workers were kidnapped and held for several days by the Achuar.
Today there is talk of sending in seismic testing teams in under military escort.
The indigenous groups say they will challenge this through legal channels, and have already taken their case to the Inter-American Court of Human Rights and the United Nations.
However, if that fails, the groups say they are prepared to fight to protect their land.