Jeff Bezos has become America’s third- richest person.

The 51-year-old founder of Amazon.com Inc. added $2.9 billion to his fortune Friday as the online retailer rose more than $35 and pushed his net worth to $53.2 billion, according to the Bloomberg Billionaires Index. Bezos passed brothers Charles and David Koch, and ranks behind only Bill Gates and Warren Buffett in the U.S.

Bezos’s fortune has jumped 86 percent in 2015 as investors have cheered profits at Amazon and growth in its cloud segment. The $24.6 billion year-to-date increase is the most of anyone on the index and almost equal to the combined gains of Facebook Inc.’s Mark Zuckerberg and Google founders Larry Page and Sergey Brin. Amazon shares surged above $600 in after-hours trading Thursday and closed at $599.03 Friday. The increase makes him the fifth-richest person on Earth, up from the No. 20 spot on Jan. 1.

The Internet entrepreneur’s soaring wealth contrasts with that of the Walton family who together control more than half of Wal-Mart Stores Inc., the world’s largest retailer. Alice, Christy, Jim and Rob Walton are among the worst-performing billionaires this year, down a combined $43.4 billion as the mass merchandiser invests in stores and e-commerce in an attempt to revitalize sales at the retailing giant.

“People don’t aspire to shop at Wal-Mart,” said Ivan Feinseth, chief investment officer at Tigress Financial Partners, who has a buy rating on Amazon and is neutral on Wal- Mart. “An improving economy is a negative for Wal-Mart. As incomes go up, people stop shopping there. Customers enjoy shopping at Amazon.”

Amazon shares represent about 93 percent of Bezos’ net worth. The closely held Koch family fortune is spread across a number of industrial companies, including paper producer Georgia-Pacific LLC, oil businesses Flint Hill Resources LLC and Koch Pipeline Company LP, as well as manufacturers of fertilizers, polymers and fibers. The asset values are calculated using revenue of $115 billion that’s reported on the website of holding company Koch Industries Inc.

The second-best performing billionaire this year is Spain’s Amancio Ortega, founder of Inditex SA, the world’s biggest clothing retailer, who’s added $16.3 billion, a 26.6 percent gain. Wang Jianlin, China’s richest person, has added $11.8 billion, a 47 percent rise. Ortega is the world’s second-richest person with $77.3 billion and Wang is 13th with $37 billion.