Microsoft co-founder Bill Gates remains America's richest man by far, as the tech and philanthropy giant took the top spot on the Forbes 400 list for the 19th year running, with a net worth of US$66 billion (NZ$79b).
Investor Warren Buffett, the head of Berkshire Hathaway, again took second with US$46 billion, while Oracle co-founder Larry Ellison remains third with US$41b and brothers Charles and David Koch, co-owners of Koch Industries, tied for fourth with US$31b.
Forbes said the rich mainly got richer in 2012, with net worth rising for 241 members of its list and shrinking for only 66. Rising stock prices, a rebound in real estate values and rare art prices helped.
More members of the Walton family, the founders of Wal-Mart Stores, moved up into the Top 10, displacing investor George Soros and Las Vegas Sands founder Sheldon Adelson.
New York City Mayor Michael Bloomberg, who made his fortune with the financial data services firm Bloomberg, is also back with the top dogs at No. 10 with an estimated net worth of US$25b.
Social media moguls took the biggest hit. Zynga's Mark Pincus and Groupon's Eric Lefkofsky dropped off the list entirely.
Facebook's Mark Zuckerberg was the biggest dollar loser in Forbes' latest ranking of the 400 wealthiest Americans. The company's lacklustre IPO in May resulted in a huge drop in market value that cut the value of his shareholdings almost in half, costing him US$8.1b in net worth. That dropped Zuckerberg from No. 14 on the list to No. 36.
But although Zuckerberg lost more money than most people will make in many lifetimes, his net worth still totals an estimated US$9.4b, according to the magazine.
Twenty newcomers joined the list, which requiredUS$1.1b in net worth for entry, up from US$1.05b a year ago. Among the freshly minted are Shahid Khan, owner of the NFL's Jacksonville Jaguars, at No. 179; Judy Faulkner, founder of health records firm Epic Systems, at No. 285; Andrew & Peggy Cherng, the husband and wife team behind restaurant chain Panda Express, at No. 239; and Twitter creator Jack Dorsey at No. 392.
There are 45 women on the list, up from 42 a year ago, including Oprah Winfrey at No. 151.
The top 10 people on this year's Forbes 400 list are:
- Bill Gates, US$66b
- Warren Buffett, US$46b
- Larry Ellison, US$41b
- Charles Koch, US$31b
- David Koch, US$31b
- Christy Walton & family, US$27.9b
- Jim Walton, US$26.8b
- Alice Walton, US$26.3b
- S. Robson Walton, US$26.1b
- Michael Bloomberg, US$25b