The world's top 100 billionaires got even richer last year, with their total wealth rising by around 15 per cent to $1.81 trillion.

Bloomberg's figures showed the world's wealthiest hundred individuals added $US241 million ($230 million) to their fortunes in 2012 for a total of $US1.9 trillion ($1.81 trillion).

Bloomberg's billionaires index shows Mexican telecommunications magnate Carlos Slim remained the world's richest person, holding a personal fortune of more than $70 billion.

Microsoft founder Bill Gates and the founder of fashion retailer Zara, Amancio Ortega, rounded out the top three spots, with wealth estimated just over and just under $60 billion respectively.

Renowned investor Warren Buffett slipped to fourth place but added around $5 billion to his fortune over the year despite donating a substantial amount to charity.

Ikea founder Ingvar Kamprad saw his net worth rise 16.6 per cent to about $40 billion, putting him in fifth place.

Just two Australians made the list: mining magnate Gina Rinehart slipped one place to 39th on the list with an 8 per cent fall in wealth to just under $18 billion, while Rupert Murdoch, who is no longer an Australian citizen, squeaked in at 96th spot due to a large rise in the value of News Corp shares last year.