The Yadana pipeline takes gas between Burma and Thailand
Energy giants Total and Chevron have been accused of propping up Burma's military government through their gas projects in the country.
Rights group Earth Rights International says this has allowed the government to siphon off $5bn (£3bn) in revenue.
The money has reportedly been stashed in banks in Singapore, instead of being used to ease poverty in Burma.
The rights group also accuses Total and Chevron of ignoring forced labour, killings and high-level corruption.
The two companies deny the allegations and say they play a positive and constructive role in communities, with development and educational programmes.
Two Singapore banks named in the report also denied involvement.
Earth Rights International has published two reports about the Yadana gas pipeline project, which transports gas overland from offshore fields to Thailand.
''Total and Chevron have essentially provided the military regime with its single largest lifeline - that being the revenue generated from the project," said Matthew Smith, the co-ordinator of Earth Rights International's Burma project.
Critics accuse the Burmese junta of numerous human rights abuses
He explained that, in research conducted over a two-year period, sources explained how the Burmese generals kept the money out of the country's budget and stored it in bank accounts in Singapore.
"Of the $4.83bn generated since 2000, approximately $4.8bn of that is not included in the national budget, and our sources indicate that the military regime is storing its illicit revenue and ill-gotten gains in two foreign banks in Singapore," he said.
The report names the two banks, but both issued statements denying involvement in Burma's Yadana project and saying the findings are untrue and without basis.
The allegation of human rights abuses are against the Burmese army which provides security for the Total and Chevron operated pipeline.
Sean Turnell, an associate professor of economics at Macquarie University in Sydney who follows energy issues in Burma closely, says the way the ruling generals make so much money raises the issue of sanctions.
''As we know, countries like the United States and Europe have fairly strict financial sanctions on Burma," he said.
"Burma's generals are able to evade these using other countries and I think what could be an interesting step forward would be for the countries that are levying these sanctions to try and pressure some of the other countries to similarly apply sanctions."
Chevron and Total are not restricted by economic sanctions imposed on Burma's rulers by the US and the European Union.
According to the BBC's Asia correspondent Alistair Leithead, there is a debate over whether sanctions should be strengthened or abandoned as an international approach towards Burma, where the majority of people live in severe poverty.