Mexican tycoon Carlos Slim, Microsoft's Bill Gates and Zara fashion house boss Amancio Ortega of Spain topped the Forbes list of the world's wealthiest billionaires Monday.

Slim, who controls Latin American telecommunications power America Movil and retail/industrial group Grupo Carso, came in first among the mega-rich for the fourth straight year, with a fortune estimated at $73 billion, up $4 billion from a year ago.

Microsoft chairman Gates, a perennial top finisher in the list,  placed second with $67 billion, up $8 billion from 2012.

Ortega, whose Inditex fashion group includes the popular Zara chain, vaulted from the seventh position into the third spot. His wealth is now estimated at $57 billion, rocketing from $31 billion a year ago.

Slim and Gates were also in the top two spots last year.

Warren Buffett, chief of US conglomerate Berkshire Hathaway, ranked fourth with $53.5 billion, and Larry Ellison, chief executive of US technology company Oracle, rated fifth with $43 billion.

Asia's richest man, Li Ka-shing, came in eighth with $31 billion. He owes to fortune to his sprawling transportation, trading and energy businesses.