A new report from the charity also found that the wealth of billionaires has grown six times faster than that of ordinary workers since 2010, with another billionaire minted every two days between March 2016 and March 2017.
Oxfam used its findings to paint a picture of a global economy in which the wealthy few amass ever-greater fortunes while hundreds of millions of people are "struggling to survive on poverty pay".
"The billionaire boom is not a sign of a thriving economy but a symptom of a failing economic system," Oxfam executive director Winnie Byanyima said in a statement.
Oxfam also emphasised the plight of women workers, who "consistently earn less than men" and often have the lowest paid, least secure jobs. Nine out of 10 billionaires are men, it added.