More London Olympics 50p coins are being hoarded by the public than any other commemorative coin circulated since decimalisation, says the Royal Mint.
The coins, produced in Llantrisant, feature Olympic and Paralympic sports.
More than £10m worth of the coins, or over 70%, will be hoarded by people wanting an Olympic souvenir, a Royal Mint audit suggested.
They are the first UK coins to be designed by members of the public.
Philip Mussell, director of Coin News magazine, said it was very unlikely the coins would be worth anything more than 50p after the Olympics.
"People are simply keeping them because they're nice things to keep," he said.
"The issue numbers of them are round about 800,000 to one million for each design, and there are 29 designs.
"After the Olympic Games are all over, are there going to be 800,000 people who want these things? I doubt it."
He said people were having great fun collecting them, which is what coin collection should be all about.
A search on online auction site eBay brought up almost 4,000 results for "50p Olympic coin", however the starting price for most appears to be not much more than face value.
The coins, which have been in general circulation since October 2010, have been designed by people from Wales and England who were picked from nearly 30,000 entries in a Royal Mint public competition.
One of the more unusual coins features an explanation of football's offside rule.
That particular design was by sports journalist Neil Wolfson, who said at the time he would be very rich if he had 50p for every time anyone asked him to explain the rule.
The Royal Mint expects and plans for 2% to 3% of new 50p coins released into circulation to be removed by collectors or simply lost.
More than 10 million of the 22 million commemorative Victoria Cross 50p coins, issued in 2006, disappeared from circulation.