Image: Michael Prince/Forbes

It's hard to think of a year where Bill Gates wasn't at the top of the Fortune 400 list, considered as the definitive annual list of America's richest.

But the Microsoft co-founder continues to be the wealthiest American for the 20th year in a row, according to the list, thanks to his total net worth of $72 billion, up $6 billion in 2012.

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In second place comes Warren Buffett with $58.5 billion, up $12 billion in 2012. Despite the 25 percent increase in personal wealth year-over-year, it's still a notable distance away from Gates, who remains a major shareholder in the company he co-founded.

Oracle chief executive Larry Ellison is worth a massive $41 billion, remaining flat year-over-year, with $41 billion, and pegs in at third place.

It's little surprise that the technology industry is rated as the second-largest sector to see billionaires in. Almost fifty names on the list are considered in the technology industry, taking a slice of 12 percent of the overall wealth pie.

Amazon's Jeff Bezos is ranked in 12th place with $27.2 billion, just behind Google co-founders Larry Page and Sergey Brin at 13th and 14th place respectively, worth a combined $49.3 billion.

Mark Zuckerberg, who ranked in at 20th place, becomes one of the youngest billionaires in the list — beaten only by Dustin Moskovitz, who is only a few days younger than Zuckerberg. The social networking giant's founder has an estimated wealth of $19 billion, thanks to Facebook's rebound on the stock market after an initially dismal year.

Current Microsoft chief executive Steve Ballmer ranks in at number 21, up two places on the same list last year, who is now worth an estimated $18 billion. Ballmer recently announced his retirement from the software company, and a replacement will be sought in the next year.

Carl Icahn, who failed to acquire computer maker Dell as part of a privatization deal, is back in the top 20 list for the first time since 2008. Dell's chief executive Michael Dell is ranked in at 25th place with $15.9 billion.

Meanwhile, everyone's favorite genius-turned-entrepreneur Elon Musk, who founded Tesla Motors, is now ranked in at 61st in the table, with a total personal wealth of $6.7 billion.

According to Forbes, the combined wealth of America's richest is worth about $2.02 trillion, or roughly equivalent to the total gross domestic product (GDP) of Russia.

Clarification at 10:35 a.m. ET: Word changes in second, third paragraph to clarify wealth increases.