The next time you're holding a dollar bill, it might be worth looking further than the big number one - you could get more bang from your buck than you expected.
Ordinary low denomination bills are raking in thousands of dollars in an online trend that is centred on the eight-digit serial number which appears on each U.S. banknote.
'Unusual' bills are being bought, sold and hunted on the website CoolSerialNumbers.com, with low serial numbers, from 00000001 to 00000100, being particularly sought after, a $1 bill with the serial number 00000002 going for $2,500.
The U.S.-based site lists all the different notes that collectors are looking out for and allows serial number fans to get in touch with one another.
Big bucks: It may not be worth $99,999,999 dollars - but the serial number means this note is likely to go for a bit more than $5
Prize money: 'Repeaters' and 'super repeaters are also highly regarded on the website CoolSerialNumbers.com
High stakes: If 'trailing nine' of 19999999 is worth $750 on the website, imagine what this prize specimen must have gone for
So it is particularly unusual to find a banknote without a serial number - and the site regularly sells error notes without serial numbers.
Collectors have long been interested in rare and flawed money - and not just in the U.S.