Buddy, can you spare a billion dollars? That's how much it took this year to make Forbes magazine's annual list of the 400 richest Americans, the first time everyone on the list was worth at least $1 billion (€786 million).

The collective net worth of the country's wealthiest people rose $120 billion to $1.25 trillion. Bill Gates, founder of software leader Microsoft, topped the list as usual, with a $53 billion net worth, while his friend and bridge partner Warren Buffett, who runs diversified holding company Berkshire Hathaway, was second with $46 billion.

Gates and Buffett are also the world's richest people, Forbes has said. Mexican tycoon Carlos Slim ranked third with $30 billion, the magazine said in March.

Third place among Americans went to casino magnate Sheldon Adelson, the chief executive of Las Vegas Sands, with $20.5 billion - up $9 billion from a year
earlier.