济低迷一次又一次地表明，在危机时期，全球投资者和外国政府会转向美国国债这个安全避风港。其他外国人显然也是如此，2008年底金融危机爆发后，他们以飞快的速度存起100元的美钞。
据 美国联邦储备委员会(Fed)的估计，流通的美元中至多有三分之二由国外持有。在向众议院一个委员会的听证会提交的书面证词中，美联储储备银行运作与支付 系统部(Division of Reserve Bank Operations and Payment Systems)负责人罗斯曼(Louise Roseman)列出了统计数据：从上世纪80年代末开始，外国持有美元的比例大幅上升。她说，90年代，全球流通中的美元以每年7.7%的速度增加，主 要是因为外国需求的增长和上世纪末需求的激增。不过，2001年美元的年增速开始回落，2008年8月底之前降到了1%以下。
罗斯曼说，过去10年来美元需求放缓的原因包括，美元对很多其他主要货币贬值，国际市场对本国经济和货币有了信心，电子支付取代了部分现金的使用，还有最近衰退的影响。
2008 年9月，形势发生了变化。当时雷曼兄弟(Lehman Brothers)和美国国际集团(AIG)倒闭，金融市场急转直下。美元的增速从2008年8月底前的0.8%上升到2008年全年令人震惊的 7.7%。强劲的增长持续到2009年，当年年底美元的流通量从2007年底的7,750亿美元增加到近9,000亿美元。截至今年5月31日，美元的流 通量为9,022亿美元，约为货币流通总量的96%。
美元的增加主要来自国外。美国国内对美元的需求在2008年秋季有所增加，当时美国人涌向银行，不过联邦政府扩大美国联邦存款保险公司(FDIC)存款保险的做法和其他行动迅速把美元需求拉回到了正常水平。
在 国际需求增长的情况下，美联储要求铸印局(Bureau of Engraving and Printing)在金融危机期间加快100元美钞的印刷，以便满足全球需求。美联储说，其中大部分美元如今仍在流通中，即使海外对100元美钞的需求回 到了正常水平。铸印局执行美联储下达的印钞命令。
The economic downturn has shown, again and again, that global investors and foreign governments turn to the safety of U.S. Treasury securities in a crisis. The same apparently goes for other foreigners, who socked away $100 bills at a rapid pace after the financial crisis struck in late 2008.
As much as two-thirds of U.S. currency in circulation is held abroad, according to Federal Reserve estimates. In prepared testimony for a House subcommittee hearing this afternoon, Louise Roseman, director of the Fed's Division of Reserve Bank Operations and Payment Systems, laid out the stats: The foreign component of currency holdings 'increased significantly' starting in the late 1980s. In the 1990s, U.S. currency in circulation world-wide grew at a 7.7% average annual rate primarily due to increases in foreign demand and a demand surge at the end of the decade, she said. But annual growth rates began to fall in 2001 and fell below 1% in 2008, through August.
Among the reasons for the slower demand over the past decade, Ms. Roseman said: 'the value of the dollar decreased against many other major currencies; international markets gained trust in their own economies and national currencies; electronic payments displaced some cash usage; and the effect of the recent recession.'
That changed in September 2008, when Lehman Brothers and AIG failed and financial markets went into a downward spiral. U.S. currency growth went from 0.8% year-to-date through August 2008 to a whopping 7.7% for full-year 2008. Strong growth continued in 2009, pushing currency in circulation to almost $900 billion by the end of that year from $775 billion at the end of 2007. As of May 31 of this year, the value of U.S. currency in circulation stood at $902.2 billion, or roughly 96% of total currency and coin in circulation.
The source of the growth was mostly foreign. Domestic demand for U.S. currency increased in the fall of 2008, as Americans rushed to their banks, but the federal government's expansion of FDIC deposit insurance and other actions quickly brought it back to normal levels.
With the higher international demand, the Fed asked the Bureau of Engraving and Printing (which executes printing orders from the central bank) to accelerate production of $100 notes during the financial crisis to meet the global needs. Most of that currency remains in circulation today, the Fed says, even though demand for $100 notes from abroad has returned to normal levels.