Federal gas tax is 18.4 cents a gallon, states add on top of that somewhere in the range of 18 to 67 cents, so under a dollar no matter where you are. The EU requires a minimum gas tax of $1.55 a gallon, but depending on the country goes over $2 a gallon.
Mostly, high gas taxes. Gas taxes in some countries in Europe are as high as gas prices in some US states.