American currency has been circulating globally for most of the 20th century, and the amount of currency in circulation increased several-fold during World War II. Large-scale printing of the United States one-hundred-dollar bill began when the Soviet Union dissolved in 1991; production quadrupled, with the first trillion-dollar printing of the bill. At the end of 2008, U.S. currency in public circulation amounted to $824 billion and 76 percent of the currency supply was in the form of $100 bills (twenty $100 bills per U.S. citizen). The amount of U.S. currency circulating abroad is controversial. According to Porter and Judson, 53 to 67 percent was overseas during the mid-1990s. Feige estimates that about 40 percent is abroad. In a New York Federal Reserve publication, Goldberg writes that "about 65 percent ($580 billion) of all banknotes are in circulation outside of the country". These figures are largely contradicted by Federal Reserve Board of Governors Flow of Funds statistics, which indicate that $313 billion (36.7 percent) of U.S. currency was held abroad at the end of March 2009. Feige calculates that since 1964, "the cumulative seigniorage earnings accruing to the U.S. by virtue of the currency held by foreigners amounted to $167–$185 billion and over the past two decades seigniorage revenues from foreigners have averaged $6–$7 billion dollars per year".