If levied, the sum would be equivalent to only 2% of the nearly $13 trillion in wealth owned by the 2,700 billionaires globally, the research group hosted at the Paris School of Economics said.

Currently billionaires' effective personal tax is often far less than what other taxpayers of more modest means pay because they can park wealth in shell companies sheltering them from income tax, the group said in its 2024 Global Tax Evasion Report.

"In our view, this is difficult to justify because it risks to undermine the sustainability of tax systems and the social acceptability of taxation," the observatory's director Gabriel Zucman told journalists.

Billionaires' personal tax in the United States is estimated to be close to 0.5% and as low as zero in otherwise high-tax France, the Observatory estimated.