The main buyers of the estimated 180,000 barrels of oil stolen each day in Nigeria are based in the Balkans and Singapore, a campaigner says.
Patrick Dele Cole, a politician from the oil-rich Niger Delta region, said 90% of the stolen oil is being shipped out of the country illegally.
He has launched a "Stop The Theft" campaign to end to the practice.
Nigeria is one of the world's biggest oil producers but most of its people remain mired in poverty.'Day of reckoning'
The campaign is seeking to have ships tracked by satellite and for the money trail to be exposed.
"Once you start asking questions and throwing light on this problem, you have solved more than 50% of the problem," said Mr Dele Cole, a veteran diplomat and former presidential adviser.
"I think you should send out a warning to those who being extremely rich, that their day of reckoning is coming."
The entire oil sector in Nigeria is riddled with corruption, says BBC Nigeria correspondent Will Ross.
Many politicians are involved, he says, with part of the proceeds being used to fund election campaigns and buy votes.
The Nigerian army is supposed to stop the thieving but, although some arrests have been made, soldiers routinely take bribes of cash or fuel to turn a blind eye to the crime, our correspondent says.
Mr Dele Cole said that about 10% of the snatched oil was being refined locally by gangs operating in the delta's creeks and swamps.
The rest is mainly going to criminal networks in Ukraine, Serbia and Bulgaria, or to Singapore, which is the world's top refiner, he said.
"It's been a problem for a long time, but when it was 50,000 barrels, people thought [it] was tolerable. Now we're at a totally different level," he told Reuters news agency
The theft of 180,000 barrels of oil a day is costing Nigeria, at current oil prices, $6bn (£3.75) a year, our correspondent notes.