At the same time, the number of people living below the World Bank's poverty line is stagnating and the number of people going hungry is rising.
The report predicted there would be at least five trillionaires worldwide within a decade.
The study was released ahead of the World Economic Forum where some 3000 attendees, including business executives, academics, government officials and civic group leaders will gather at the annual meeting in the alpine village of Davos in Switzerland.
The Swiss village of Davos will host the annual meeting of World Economic Forum. (AP PHOTO)
Oxfam's research adds weight to a warning by outgoing US President Joe Biden last week of a "dangerous concentration of power in the hands of very few ultra-wealthy people".
The group's report, titled 'Takers Not Makers', says the number of people in poverty has barely budged since 1990.
US President-elect Donald Trump, who will take the oath of office on Monday (Tuesday AEDT), is expected to take part in the forum's event by video on Thursday.
He has long championed wealth accumulation — including his own — and counts the world's richest person Elon Musk as a top adviser.
"What you're seeing at the moment is a billionaire president taking oaths today, backed by the richest man. So this is pretty much the jewel in the crown of the global oligarchies," Amitabh Behar, executive director of Oxfam International, said in an interview, referring to Trump and Musk.
The Oxfam report is based on data from sources including estimates of the wealth of billionaires made by the US business magazine Forbes and data from the World Bank.
Business executives, academics and government officials will meet at the World Economic Forum. (AP PHOTO)
According to the report, billionaire wealth rose from $US13 ($A21) trillion to $US15 ($A24) trillion in 2024 alone worldwide, a growth rate three times faster than the previous year.
On average, the wealth of a single billionaire increased by $US2 million ($A3.2 million) a day.
The richest 10 billionaires became richer by an average of $US100 million ($A161 million) per day. Even if they were to lose 99 per cent of their wealth overnight, they would still remain billionaires, Oxfam said.
The report also highlighted how the source of 60 per cent of billionaire wealth is "inheritance, monopoly power or crony connections".
Worldwide, 36 per cent of billionaire wealth is derived from inheritance, according to Oxfam.
This is even starker in the European Union, where 75 per cent of wealth is unearned, with 69 per cent of wealth coming from inheritance alone.
"Billionaire wealth is exploding, and the bottom line is most wealth is not earned, it is inherited," said Oxfam EU tax expert Chiara Putaturo.
"Meanwhile, the number of people in poverty worldwide has barely budged since the nineties," she said.
"EU leaders need to tax more the wealth of the super-rich, including inheritance. Without this, we risk seeing the gap between the ultra-rich and ordinary Europeans growing."
with AP
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