The horror of $4/gallon gasoline in the US is a pipe dream to Europe. Even in 2004, when the dollar was stronger and the price of gas decidedly lower, The Monk paid $5.70/gallon in the UK (based on about 80p per liter and a 1.80/1 exchange rate USD/GBP). In 2007, when The Monk took Monkette on our babymoon, we paid $5.35 /gallon for diesel (gasoline was $6.85) in France, based on the $1.30/1 USD/Euro exchange rate. And for the Euros, those were the good old days.
This site says the average price for premium gasoline, per gallon in USD, was more than $8.70 in France, Belgium, Italy, Netherlands, Germany and UK last week. Take off 70 cents per gallon for a lower fuel grade, and none of those major European countries had a per gallon cost of less than $8. That makes Japan, with prices around $6.50-7 per gallon, look affordable.
Why so expensive? Taxes. In the UK, when we paid 80p per liter, about 65-67p went to the government. Taxes remain high, and refining costs have also escalated as the global oil price has risen.
And that's why The Monk liked taking the train so much in Japan.