San Francisco: Jeff Bezos just became America’s third- richest person.

The 51-year-old founder of Inc. has so far added almost $5 billion to his fortune as the online retailer rose in after-hours trading and pushed his net worth above $55 billion, according to the Bloomberg Billionaires Index. Bezos passes brothers Charles and David Koch, and ranks behind only Bill Gates and Warren Buffett in the US.

Before Thursday’s surge, Bezos’s fortune had jumped 77% in 2015 as investors have cheered profits at Amazon and growth in its cloud segment. The $22 billion year-to-date increase is the most of anyone on the index and more than the combined gains of Facebook Inc.’s Mark Zuckerberg and Google founders Larry Page and Sergey Brin. Amazon shares rose 10% from the close to $621 at 4:47pm in New York. The increase will make him the fifth-richest person on Earth, up from the No. 20 spot on 1 January.

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 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 95% 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 $15 billion, a 24% gain. China’s richest person, Wang Jianlin has added $11 billion, a 44% rise. Ortega is the world’s second-richest person with $76 billion and Wang is 12th with $36 billion.

The Bloomberg Billionaires Index is a daily ranking of the world’s richest people that’s updated every business day. It uses prices at the market close in New York to derive the value of publicly traded assets. Thursday’s list doesn’t reflect after-hours trading. Bloomberg