Taking the gross domestic product of both economies in 2007, the combined GDP of the 15 countries which use the euro overtook that of the United States when the European currency surged to a record high of more than $1.56 per euro.
"The curious outcome of breaching this latest milestone is that the size of the euro zone's annual output has now exceeded that of the U.S.," the economics department of Goldman Sachs, the Wall Street investment bank, said in a note to clients.
Taking official estimates of 2007 GDP -- $13,843,800 billion for the United States and 8,847,889.1 billion euros for the euro zone -- the economy of the latter passed the United States once converted into dollars, shortly after the euro topped $1.56.
The dollar sank to $1.5688 per euro late in European trading hours on Friday, at which rate the euro zone's 2007 GDP equates to $13,880,568.4 billion.
The 2007 GDP estimates are as published by the U.S. Commerce Department's Bureau of Economic Analysis and provided to Reuters on request for the euro zone by Eurostat, the European Union's statistics office.