The aggregate net worth of the world's top billionaires was $3.7 trillion at the market close Dec. 31, the daily index of the world's 300 wealthiest individuals reported, with the top 300 adding $524 billion to their collective net worth.
Of the 300 people who were in the final ranking of 2013, only 70 registered a net loss for the 12-month period, the index reported Thursday.
Gates, founder and chairman of Microsoft Corp., based in Redmond, Wash., increased his wealth by $15.8 billion to $78.5 billion, the index indicated, as shares of Microsoft rose 40 percent.
Sheldon Adelson, political contributor and founder of Las Vegas Sands Corp., was the second-biggest gainer in 2013, adding $14.4 billion to his net worth, the index said.
The Bloomberg Billionaires Index said Gates reclaimed the title of world's richest person May 16 from Mexican investor Carlos Slim, who lost money in 2013 but still was among the rich who added to their wealth.
Slim was $51 billion ahead of Jorge Paulo Lemann, Latin America's second-richest person and Brazil's wealthiest, the index indicated.