The charity's research shows that the share of the world's wealth owned by the richest 1% increased from 44% in 2009 to 48% last year.
On current trends, Oxfam says it expects the wealthiest 1% to own more than 50% of the world's wealth by 2016.
The research coincides with the start of the World Economic Forum in Davos.
The annual gathering attracts top political and business leaders from around the world.
Oxfam's executive director Winnie Byanyima, who will co-chair the Davos event, said she would use the charity's high-profile role at the forum to demand urgent action to narrow the gap between rich and poor.
In a statement ahead of the gathering, Ms Byanyima said the scale of global inequality was "simply staggering".
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