Leading the pack are Jeff Bezos and Mark Zuckerberg, whose fortunes grew by $34.6 and $25 billion respectively, according to the Americans for Tax Fairness and the Institute for Policy Studies' Program for Inequality - based on Forbes data for America's over 600 billionaires collected between March 18 and May 19.

Percentage-wise, Elon Musk's wealth grew 48% to $36 billion, while Zuckerberg clocked in at 46%. Bezos' wealth grew 31% to $147 billion. His ex-wife, MacKenzie Bezos, saw her wealth increase by roughly 33% to $48 billion. On average, American billionaires saw their net worth grow 15% during the two-month period from $2.948 trillion to $3.382 trillion.

Bezos, Bill Gates, Zuckerberg, Buffett and Larry Ellison saw combined gains of $76 billion.