Facebook set an opening share price of $38 on Thursday evening, which valued Zuckerberg's 503.6 million shares and options at about $19.1 billion. Trading opened on Friday at about $42.
That price would make Zuckerberg's portion of the company worth $21.2 billion.
The 28-year-old CEO would be not only more wealthy than Google founders Sergey Brin and Larry Page, but also creeping into the territory of Amazon CEO Jeff Bezos, who holds the number 23 spot.
Shares dipped back to $38 almost immediately after the stock opened and will likely fluctuate -- along with Zuckerberg's net worth -- throughout the day. The Wall Street Journal has set up a real-time "Wealth-o-Meter" for those interested in following along.
Zuckerberg had planned to sell 30.2 million of his shares in the IPO, which would net him $1.3 billion at Friday's opening trading price. According to Facebook's filing with the SEC, he will use most of the proceeds to pay taxes associated with exercising 60 million stock options.
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