Photo: The Canadian Press. All rights reserved.

This June 26, 2012 image provided by Forbes, and the pull-out cover for the magazine's Sept. 21 issue shows from left to right: Warren Buffett, Oprah Winfrey, Bill Gates, Melinda Gates, Pete Petersen, Leon Black, Jon Bon Jovi (seated on the ground), Marc Benioff, David Rubenstein, Steve Case, Laura Arrillaga-Andreessen, Marc Andreessen posing for a portrait in the Trustees Room at the New York Public Library in New York. The twelve individuals shown were part of a group attending a Forbes convened event called the Forbes 400 Summit On Philanthropy. philanthropists in the U.S. to pose for the portrait. (AP Photo/Forbes, Michael Prince)

Microsoft Corp. co-founder Bill Gates remains the nation'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 $66 billion.

Investor Warren Buffett, the head of Berkshire Hathaway Inc., again took second with $46 billion, while Oracle Corp. co-founder Larry Ellison remains third with $41 billion and brothers Charles and David Koch, co-owners of Koch Industries Inc., tied for fourth with $31 billion.

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 Inc., moved up into the Top 10, displacing investor George Soros and Las Vegas Sands Corp. founder Sheldon Adelson. New York City Mayor Michael Bloomberg, who made his fortune with the financial data services firm Bloomberg LP, is also back with the top dogs at No. 10 with an estimated net worth of $25 billion.

Social media moguls took the biggest hit. Zynga Inc.'s Mark Pincus and Groupon Inc.'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 $8.1 billion 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 $9.4 billion, according to the magazine.

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:

1. Bill Gates, $66 billion
2. Warren Buffett, $46 billion
3. Larry Ellison, $41 billion
4. Charles Koch, $31 billion
5. David Koch, $31 billion
6. Christy Walton & family, $27.9 billion
7. Jim Walton, $26.8 billion
8. Alice Walton, $26.3 billion
9. S. Robson Walton, $26.1 billion
10. Michael Bloomberg, $25 billion

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