A global super-rich elite had at least $21 trillion (£13tn) hidden in secret tax havens by the end of 2010, according to a major study.
The figure is equivalent to the size of the US and Japanese economies combined.
The Price of Offshore Revisited was written by James Henry, a former chief economist at the consultancy McKinsey, and commissioned by the Tax Justice Network.
He said $21tn is a conservative figure and the true scale could be $32tn.
A trillion is 1,000 billion.
Mr Henry used data from the Bank of International Settlements, International Monetary Fund, World Bank, and national governments.
His study deals only with financial wealth deposited in bank and investment accounts, and not other assets such as property and yachts.
Private wealth held offshore represents "a huge black hole in the world economy," Mr Henry said.
A little "service charge" on these accounts could probably clear the global debt crisis!