The Angolan government has been asked to explain the disappearance of $US32 billion.
The discrepancy was uncovered by a team from the International Monetary Fund, but the information was buried in an IMF report.
It includes $US7.1 billion transferred into escrow accounts overseas and $US24.9 billion described as "an unexplained discrepancy in government accounts".
The IMF said the money disappeared between 2007 - 2010.
The Human Rights Watch group previously identified more than $US4 billion in oil revenues that went missing from government accounts between 1997 - 2002.
