The rich are getting richer at a fast clip, with the Oracle of Omaha, Warren Buffett, leading the pack, adding $37 million to his wealth every day so far this year, according to Wealth-X.
According to a study by Wealth-X, which researches the ultra-wealthy, on how much billionaires' wealth has grown this year, Buffett earned $12.7 billion in the first 345 days of the year, bringing his total net worth to around $59.1 billion.
But while he's been the fastest earner so far this year, Buffett isn't the world's wealthiest. The annual widely-quoted ranking of the world's wealthiest people, compiled by Forbes magazine in March, ranks him in fourth place.
But Buffett's fresh earnings suggest he may be able to contest third place against the founder of clothing retailer Inditex, Amancio Ortega -- who didn't make Wealth-X's list of the billionaires with the highest earnings for this year.
The 83-year-old Buffett's earnings outpaced earnings by the 58-year-old Bill Gates, who ranks second on Forbes' list. Wealth-X found the Microsoft founder added another $11.5 billion to his cache, bringing the total to $72.6 billion, which puts him in the running to challenge the family of Mexican telecoms magnate Carlos Slim for the top spot on Forbes' billionaire list. Slim's earnings didn't make Wealth-X's top-10 list.
Casino mogul Sheldon Adelson may have a shot at leapfrogging into the top-10 on the Forbes list from his spot at number 15 back in March. According to Wealth-X, the 80-year-old CEO of Las Vegas Sands proved gambling pays off for the house, adding another $11.4 billion to his personal fortune, bringing it to $35.3 billion.
Hot on his heels, Amazon founder Jeff Bezos has another $11.3 billion of coins jingling in his pockets, delivered without drones, bringing his total to $34.4 billion, Wealth-X said.
The tech sector's leading lights dominate the list, with other names including Larry Page and Sergey Brin from Google, Softbank CEO Masayoshi Son and Facebook founder Mark Zuckerberg.
Another casino mogul, Lui Chee Woo, who controls Macau casino operator Galaxy Entertainment, ranked at number nine, tacking $8.3 billion onto his personal fortune, bringing his net worth to $19.6 billion, according to Wealth-X. In March, Forbes ranked him at only the 98th richest person globally, but his earnings may leapfrog him into the top 40.
All in, billionaires have had a good year.
In November, Wealth-X and UBS Global Billionaire Census for 2013 found billionaires' combined fortunes have grown by $226 billion in the past year alone. They have more than doubled to $6.5 trillion from $3.1 trillion in 2009 and the group expanded by 810 over the period to 2,170 members, the census found.
(Read more: Asia's billionaire club grows as Europe's shrinks)
Their total wealth is now larger than the gross domestic product of any country except the United States and China, and could fund the U.S. budget deficit until 2024, the census found.
The average billionaire spends $22 million on yachts, $16 million on private planes and $14 million on art, according to the census.
In the U.S., the wealthy are now hoarding their highest proportion of assets in nearly a hundred years.
The top 1 percent's share at the end of 2012 was equal to 50.4 percent of the U.S.'s overall wealth, a level higher than any other year since 1917 and surpassing 1928, the peak of stock market bubble in the "roaring" 1920s, according to Emmanuel Saez, a professor of economics at the University of California, Berkeley.
Since the financial crisis of 2008, the top 1 percent of incomes have grown by 31.4 percent while the bottom 99 percent of incomes has grown only by 0.4 percent, he said.
—By CNBC.Com's Leslie Shaffer; Follow her on Twitter