I just ran across a great blog post offering a comparison between U.S. and European Gas Prices, I talked about this a little in the past in my blog post on "Truth in advertising and the gas tax..." but Jason Morgan, the author of this particular blog post does a more complete break down of the overage price differential and finds that Europeans on average pay $0.95 LESS per gallon for gas (when you leave the taxes out).
He also interestingly points out that this difference, which works out to 26.7%, is almost exactly the same as the depreciation the U.S. Dollar has experienced against the Euro over the past five years (27%).