I would assume they are but I can't see how there would be that many. Are each serial numbers unique or are they only unique by denomination? Lilke, could you find the same SN in a $1 and $10? I want to track my bills and I need a unique way to do it.

Serial numbers are not absolutely unique, as I suppose they could be duplicated between series (i.e. you have a series 1999 $1 with the same serial number as a series 2003 bill). As long as you include the series as well as the serial number for $1, $2 or old style bills of $5 and higher you will have a unique identifier. On the new style bills, all the serial numbers are unique since there is a 2-letter prefix for each, with the first letter as a code for the series, so all series 1996 notes begin with A, 1999 begin with B, 2001 begin with C, 2003 begin with D, 2004 begin with E, etc. The second letter denotes the Federal Reserve bank that issued the note (A=Boston, B=New York, C=Philadelphia, D=Cleveland, E=Richmond, F=Atlanta, G=Chicago, H=St. Louis, I=Minneapolis, J=Kansas City, K=Dallas, L=San Francisco). So on the new notes, the serial numbers cannot possibly repeat since the first letter will change with each series (though I am not sure what will happen when they get to Z!). On $1 and $2 and older style notes, the first letter in the serial number denoted the FRB of issuance. Hope this helps.

Serial numbers are most definately not unique, BUT each banknote is unique, as in, you can have the same serial numbers with different banknotes, like 1 dollar and 20 dollars. You can also have the exact same serial numbers with the same currency except that the production date differs.

I have only seen one collection that features that, just because the retarded collector only collects straight numbers...

Guess I will have to make up my own # scheme. I will probably formulate something like (year)(demoniation)(last-four SN)