After World War II the United States held 80 percent of the world's gold stocks.

Taken as the US share of the world's official (monetary) gold reserves after WWII (around 1945–1950). True: historical data show a US share of about 75–80% or more at its post-war peak. Mostly true: a share of about 65–75% at the peak, or about 80% only of non-communist or central-bank gold. Mixed: estimates vary widely around the claim (some about 60%, others about 80%). Mostly false: the share was about 50–65%. False: the share was below about 50%.

Set before the research began.

1. E1 Bretton Woods and the U.S. Decision to Intervene in the Foreign-Exchange Market, 1957–1962 Federal Reserve Bank of Cleveland (Working Paper 06-09, by Michael D. Bordo, Owen F. Humpage, and Anna J. Schwartz) · August 2006

   “The United States, which held 60 percent of the world’s gold reserves in 1950, lost only $213 million worth of gold on average each year between 1950 and 1957 (figure 4).”

2. E2 Bretton Woods and the U.S. Decision to Intervene in the Foreign-Exchange Market, 1957–1962 (Working Paper 06-09) Federal Reserve Bank of Cleveland (authors Michael D. Bordo, Owen F. Humpage, Anna J. Schwartz) · August 2006

   “The United States, which held 60 percent of the world’s gold reserves in 1950, lost only $213 million worth of gold on average each year between 1950 and 1957 (figure 4).”

3. E3 [PDF] Statement of - FRASER - Federal Reserve Bank of St. Louis Federal Reserve Bank of St. Louis (FRASER), reproducing William McChesney Martin Jr.'s statement as Fed Chairman · 1 February 1965

   “Gold certificate reserves of the Federal Reserve Banks reached their peak of $23. 4 billion in September 1949 when the total U, S. gold stock amounted to about 70 per cent of the free world !s monetary gold.”

4. E4 7. THE MONETARY SYSTEM AND THE CONTRADICTIONS OF CAPITALISM libcom.org (reprinted text, original author not shown on the fetched page) · 26 February 2017

   “World monetary gold (exclusive of socialist countries) in 1949 totalled $ 35,055 million, of which $ 24,563 million, or 70 per cent, were in the United States;”

5. E5 7. THE MONETARY SYSTEM AND THE CONTRADICTIONS OF CAPITALISM libcom.org (reprinted text, original author not shown on the fetched page) · 26 February 2017

   “In 1951 the United States had a stock of monetary gold amounting to $ 22,873 million, or 64.3 per cent of the world total ($35,575 million).”

6. E6 Gold Reserves Main Holders 1948-2008 Scribd (uploaded document; original data source not shown)

   “United States 21,682.4 21,828.2 20,279.3 20,326.3 20,663.1 19,631.4 19,366.7 19,331.0 19,602.2 20,312.3 18,290.6 17,335.1”

The evidence gives US shares of about 70 percent of the free world's monetary gold in 1949 (E4, E5), 60 percent of world gold reserves in 1950 (E1, E3) and 64.3 percent in 1951 (E6). It does not cover 1945 to 1948, so it does not show the post-war peak share that the criteria ask for.