The Eurozone and the USA both have a population of almost exactly 300 million. But given that the hundred-dollar bill is the currency unit of choice in countries with less-than-stable currencies of their own, it's hardly surprising that there are a lot more paper dollars in circulation than there are paper euros.

Except it now looks as though the euro has overtaken the dollar: Ralph Atkins reports in the FT that the value of euro notes looks like it's going to hit $800 billion at present exchange rates, overtaking the $759 billion of dollar notes in circulation.

I can think of five main reasons:

• The strength of the euro against the dollar. The €610 billion in euros in circulation is still a smaller number than $759 billion, so this small landmark has more to do with FX rates than with printing presses.
• Eurozone citizens carry more cash. I have no idea if this is true or not.
• The euro has replaced the dollar as what you might call the "retail reserve currency" in most of non-Eurozone Europe, including, crucially, Russia. If you're an Estonian wanting to keep your savings in something safe, you're more likely to want euros than dollars.
• There are a lot of euros floating around in non-Eurozone EU Western European countries, especially Britain, Denmark, Sweden, Norway, and Switzerland. Citizens of these countries travel regularly to the eurozone, and are likely to have a fair amount of euro cash lying around. And of course the population of the EU, if not of the eurozone, is much larger than the population of the US.
• The €500 note – worth more than $650 – is a much more convenient and pocketable carrier of value than the $100 bill. If you want to carry large amounts of cash, you're much better off with euros, no matter where you are in the world.

(Via Dean Baker)