South Sudanese oil now sells at $20-25 a barrel, possibly the lowest rate on Earth, according to a report by the London-based Financial Times newspaper.

"South Sudanese revenues have now fallen to about $100m a month, equal to an oil price of about $20.5 per barrel based on output of 160,000 barrels a day," the FT report said.

Citing traders as well as unnamed South Sudanese and foreign officials, the report attributes the drop to low oil prices worldwide and high pipeline fees paid by Juba to Khartoum.

Oil prices have plummeted in recent months thanks to a surge in petroleum production in the United States, where new 'fracking' technology enables drillers to reach previously hard-to-get fossil fuel deposits.

However, South Sudan pays a fixed rate of $26 per barrel for use of Sudan's pipelines regardless of market value, as per a 2012 agreement between the two countries.

South Sudanese oil is also cheaper due to its quality. The government in Juba earns over 90% of its revenue from oil sales.

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