(CNBC) The amount of $100 bills in circulation is surging. And it's leaving some economists scratching their heads.
The number of outstanding U.S. $100 bills has doubled since the financial crisis, with more than 12 billion of them across the world, according to the latest data from the Federal Reserve. C-notes have passed $1 bills in circulation, Deutsche Bank chief international economist Torsten Slok said in a note to clients this week.
Generally, economists believe the surge is related to people around the world wanting to hoard cash, a similar force that's driven the interest in cryptocurrencies. High denomination, high value currency notes have historically been a preferred form of payment for criminals, given the anonymity, lack of transaction record and relative ease with which they can be brought across borders.
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