THE world's 100 richest people got even richer last year, building their collective wealth to $US1.9 trillion. But the fortunes of the two Australians to make the cut - Gina Rinehart and expat Rupert Murdoch - were mixed.

Rinehart, Australia's richest person, dropped one rung to rank 39th on the Bloomberg Billionaires Index, with her $US18.6 billion fortune falling 8 per cent, or $US1.6 billion - partly due to softer iron ore prices last year, and partly due to losing investments in media companies including Ten Network and Fairfax Media, owner of The Age. Ten and Fairfax shares fell 56 per cent and 29 per cent respectively last year, and Rinehart lost an estimated $150 million on her substantial stakes in each company.

By contrast Rupert Murdoch's wealth jumped by $US2.9 billion to $US10.7 billion, courtesy of a 44 per cent rise in the value of his News Corporation shares as the company rebounded from the 2011 phone-hacking scandal that led to the closure of the News of the World in Britain, and investors reacted positively to the proposal to spin off the company's publishing assets from the profitable Fox Group, as News will be renamed.

The aggregate worth of the world's top moguls grew by $US241 billion to $US1.9 trillion at December 31, according to the Billionaires Index, a ranking of the world's 100 wealthiest individuals.