NEW YORK (AP) - 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. Brothers Charles and David Koch, co-owners of Koch Industries Inc., tied for fourth with $31 billion.

Forbes says 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.

Facebook's lackluster IPO dropped Mark Zuckerberg from No. 14 on the list to No. 36.