Thieves puncture pipelines with farm tools, siphon oil into boats, and take it to risky makeshift refineries.
Goodluck Jonathan, the Nigerian president, has called the stealing of the country's oil an "embarrassment" to his nation. To many people in oil-producing regions, however, the crude that is siphoned from fuel company pipelines is the one thing they depend on.
A recent Al Jazeera report has found that fishing and farming, the two main economic activities in the oil-rich Niger Delta, are now all but abandoned. Frequent oil spills have depleted fish species in rivers and streams while millions of hectares of farmland lie wasted by oil pollution and contamination.
In some parts of the Delta, stealing oil from the pipelines has become a free-for-all. Sometimes entire villages are involved.
The oil thieves attack the underground pipelines with saws and hammers and then siphon off the oil in boats or barges.
The government and oil companies say they are losing more than $1bn a month to the crime, and that loss has reportedly risen sharply under Jonathan's administration.
Ngozi Okonjo-Iweala, Nigeria's finance minister, has said the trade in stolen oil has led to a fall in official sales of about 400,000 barrels a day - a 17 per cent drop - in April alone. With average April prices of $121 per barrel, this results in a loss of $1.4bn.
This is a higher estimate than that given by Royal Dutch Shell's Nigerian subsidiary, which put loss from theft at between 150,000 and 180,000 barrels a day.
According to the authorities, the trade in stolen oil also involves sophisticated criminal networks and international traders who provide oil at discounted prices to refineries in West Africa, China and India.
Dangerous process
In Bayelsa State, Al Jazeera met a group of youth refining, or "cooking", the crude - as they like to call it.
The contraption they loosely call a refinery looks like a grade-school science project. The aim is to boil two barrels of oil to evaporate the fuel, which then passes down a rusted pipe, cooled by water, and drips slowly out into a container at the other end.
The petrol comes out first, then kerosene, and finally diesel. Whatever remains of the crude is then poured into the river. It is a very dangerous business. With naked flames just metres away from the fuel, there are frequent explosions and many deaths. The surrounding trees and earth are blackened from the flames and explosions.
Their haughty leader, Ibegi Alakoroa, is unrepentant.
"It's mainly because of anger we are doing this job, because the government and oil companies don't recognise us," he told Al Jazeera. "We want to tell the politicians that Nigeria's oil is for all of us. They eat the oil revenue in Abuja and we take the crude down here. That’s how it's going to be."
The rough fuel that is refined here also finds a ready market within nearby communities and towns. Nigeria's legal refineries are largely non-operational and fuel shortages are very common.
'Cleaning up'
It is the environmental damage the stealing and "cooking" of oil in Nigeria that is most profound. Flying low over the oil-producing Niger Delta, Al Jazeera witnessed what is effectively a crime scene: rivers and streams covered by thick filmy layers of oil. Vegetation in this once heavily forested region has also been devastated by frequent oil spills and explosions.
We were taken on the aerial tour by Shell, the biggest oil company in Nigeria, which was keen to point out the environmental damage caused by oil theft and illegal refineries.
There is so much damage, Shell now says its "priorities have changed".
"Cleaning up what has already occurred would be futile unless you stop more from happening and I think that is where the challenge is," said Dr Philip Mshelbila of Shell Nigeria.
"It's not so much the cleanup, but it's the stopping of new spills from occurring in either already contaminated areas or new areas," he added.
Shell, one of the largest corporations on the planet, last year admitted its own liability in two devastating oil spills in the Ogoniland region - an area which has seen frequent and long-running unrest, with Ogoni activists accusing the oil giant of human rights violations spanning decades. The spills, in 2008, were reported to be potentially as large as the Exxon Valdez disaster, in which 11 million gallons of oil destroyed 1,300 miles of Alaska's coastline in 1989."
Theft resumes
In recent months, the Nigerian army has been deployed to quell the growing lawlessness in the country's oil-producing areas. They've burned down makeshift refineries and arrested hundreds of suspects.
Lieutenant Colonel Onyema Nwachukwu, a spokesman for the task force charged with stopping oil theft, said the authorities are targeting everyone involved in the illicit activity.
"Nobody is going to be spared [no matter] of his position, status, no matter how highly placed. We have the mandate to carry out our duties and that is why we are here. We are here to protect the oil and gas sector of Nigerian economy," he told Al Jazeera.
The oil thieves vow that not even the military will stop them.
"Each day they continue burning our refineries, but we say: 'Let's go back to the job again and we go back immediately,'" said Alakoroa.
The criminal networks profiting from stolen oil have their tentacles deep within the state power structure, said Inemo Samiama of the Stakeholder Democracy Network. The re-routed oil is believed to help finance a system of patronage which keeps the political system afloat.
Observers such as Samiama have said the complicity of corrupt security officials and politicians means the theft of Nigeria's crude oil is unlikely to end any time soon.
Source: Al Jazeera