NEW YORK (Reuters) - Things are on the up for U.S. billionaires with more than half of them adding to their net worth in a year which once again saw Bill Gates as the richest of them all, Forbes magazine said on Wednesday.

Bill Gates attends a news conference to promote the film "Waiting For Superman" during the 35th Toronto International Film Festival September 11, 2010. REUTERS/Fred Thornhill

Gates, founder of Microsoft, was the richest person in the United States for the 17th year in a row with an estimated worth of $54 billion, up $4 billion from last year.

No. 2 on the list was investor Warren Buffett, worth $45 billion, up $5 billion. Oracle founder Larry Ellison’s net worth was unchanged, in third place, at $27 billion. Christy Walton, heir to Walmart founder Sam Walton’s fortune, was in fourth place with $24 billion, up $2.5 billion.

In stark contrast to the 2009 Forbes 400 list, 217 of the tycoons are now worth more than they were a year ago. Just 84 of the billionaires had a decrease in wealth.

In 2009 a whopping 314 members of the exclusive club had experienced a decrease in their wealth.

The top 10 gained $24.9 billion. The same group had shed almost $40 billion last year.

The total wealth of the group is up 8 percent, besting the Standard & Poor’s 500 index, which measured a stock market increase of just 1 percent, Forbes said.

The Forbes 400 are worth a combined $1.37 trillion, compared with $1.27 trillion last year.

The price of admission to the list is back up to $1 billion from 2009 when $950 million was enough to make the top 400.

There are no new entries or drop-offs in the top 10 but the list shuffled. The Koch brothers, heads of energy and manufacturing giant Koch Industries, now rank above three other members of the Walton family and New York Mayor Michael Bloomberg, founder of news and information company Bloomberg LP, who round out the top 10.

Facebook’s Mark Zuckerberg, No. 35, saw the largest relative increase, more than tripling his fortune to $6.9 billion from $2 billion. Fellow Facebook co-founders Dustin Moskovitz and Eduardo Saverin join the list with fortunes of $1.4 billion and $1.15 billion, respectively. Born eight days after Zuckerberg, 26-year-old Moskovitz is the world’s youngest billionaire.

The oldest tycoon on the list is David Rockefeller Sr., 95, worth $2.4 billion.

Media magnate Oprah Winfrey comes in at No. 130 and is one of 42 women on the list.

Automobile heir William Ford Sr. made the list for the first time since 2005, at the 385th spot with $1 billion after Ford Motors Co’s stock rose 50 percent and hit a 5-year-high.

California is the state with the most billionaires -- 83 -- among them No. 332 Meg Whitman, worth $1.2 billion, the Republican candidate for governor of the state in November elections.

The full Forbes 400 list can be seen at www.forbes.com/Forbes400.