The combined wealth of 10 men increased during the coronavirus pandemic by $540bn (£400bn), Oxfam has found.
This amount would be enough to prevent everyone in the world from falling into poverty because of the virus and pay for a vaccine for all, the NGO said.
Its report found the total wealth of billionaires was equivalent to the entire spending by all G20 governments on recovering from the virus.
The charity is urging governments to consider taxes on the super-rich.
The report, the Inequality Virus, has been published as global leaders gather virtually for the World Economic Forum's "Davos Dialogue" meeting.
Unprecedented support from governments for their economies saw the stock market boom, driving up billionaire wealth while the real economy faces the deepest recession in a century, it says.
Worldwide, billionaires' wealth increased by $3.9tn (trillion) between 18 March and 31 December 2020 and now stands at $11.95tn - which is equivalent to what G20 governments have spent in response to the pandemic, the report says.
The 10 richest people, whose fortunes rose by $540bn since March 2020, include Amazon founder Jeff Bezos, Tesla founder Elon Musk and Facebook founder Mark Zuckerberg.

The report said that Mr Bezos had earned so much by September 2020 that he could have given all 876,000 Amazon employees a $105,000 bonus and still been as wealthy as he was before the pandemic.
This compares with the world's poorest, for whom recovery could take more than a decade. Oxfam estimates that as many as 500 million more people were living in poverty as a result of the pandemic, reversing the decline in global poverty seen over the last two decades.
"We think that this is ... an opportunity to do something radical about building back fairer to think about wealth taxes, to think about corporation taxes, to think about increasing the basic social floor for every citizen," Danny Sriskandarajah, Chief Executive of Oxfam GB, told the BBC.
With reference to the UK, he said imposing a tax could raise millions.

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