Even when a gallon of regular gasoline passes the $4 mark in the U.S., American drivers still pay less than half of what it costs to fuel up in Europe. Throughout much of Europe, gas costs the equivalent of $8 or more per gallon, due at least partially to high gasoline taxes. Lately, Norway has laid claim to the dubious title of pumping the world’s most expensive gas, generally running over $9 per gallon. The only time drivers in the U.S. may encounter such prices is when they are charged penalty rates by car-rental agencies when they don’t prepay for gas or fill up the car before returning it.