In January 1999, the U.S. mint sold 208,500 gold 1-ounce coins, with only five other months exceeding May's gold coin sales since the program was launched in 1986.
While in 2010 the U.S. Mint has sold only 1-ounce gold coins, in past years it has sold other coin sizes as well.
Comparing only American Eagle gold 1-ounce coins, the biggest monthly sale occurred in October 1986 with 609,500 coins sold, the Mint said.
Many investors, both retail and institutional, have sought gold as a safe-haven asset in times of economic uncertainty. Sales of the American Eagle coins increased by 214 percent in the month over April during a time when concerns about sovereign debt in the euro zone raised fears of a larger macro-economic effect.
The price of gold bullion reached a record high last month at $1,248.95 per ounce.