It takes just four days for a CEO of one of the world's five biggest fashion retailers to earn as much as a Bangladeshi garment worker will earn in her entire lifetime, the report added.
Separate figures released this month by The High Pay Centre show that in 2017 it took just three days for the UK's top bosses to make more money than the typical British full-time worker will earn all year.
Mark Goldring, Oxfam's chief executive, said: "Something is very wrong with a global economy that allows the 1 per cent to enjoy the lion's share of increases in wealth while the poorest half of humanity miss out.
"The concentration of extreme wealth at the top is not a sign of a thriving economy but a symptom of a system that is failing the millions of hard-working people on poverty wages who make our clothes and grow our food."
Goldring continued: "Some companies and wealthy individuals are taking steps towards fairer ways of doing business but too many others use their power to protect their own interests. To really transform our economies, we need to look again at the business models and laws that prioritise shareholder returns above wider social benefit."
Oxfam has produced similar reports for the past few years. In 2017 it calculated that the world's eight wealthiest people owned as much wealth as the poorest half of the world. It later revised the figure to 61, claiming access to improved data.
A report by The Institute for Policy Studies last year showed that the three wealthiest people in the United States – Bill Gates, Jeff Bezos, and Warren Buffett – own more wealth than the entire bottom half of the American population combined, a total of 160 million people.
The three business moguls have a total wealth of US$248.5 billion ($339b), while America's top 25 billionaires together hold US$1 trillion in wealth – about the same amount as 56 per cent of the US population combined.