Mjollnir is correct, the difference is taxes. U.S. motor fuel taxes are very low (US$0.0486/liter in federal excise tax [as of 1998] plus from US$0.0198/l to US$0.0845/l in state taxes [as of 1 Jun 00]). In contrast, European motor fuel taxes not so low. For example, in the Netherland, per liter taxes apparently amount to US$0.5486/l and there is a VAT of 17.5%.
Oil is a globally traded commodity. Like other globally traded commodoties, such as sugar, copper, gold, coffee, etc., it is produced in many places around the world and consumed all over the world. Like other globally traded commodities, its global price depends on the balance of global production and global demand.
The local price of motor fuels (exclusive of duties and taxes) is determined mainly by the global price of oil. Transport costs don’t play much of a part (unless you are living on a remote island or mountain top) since just about all oil hass to be shipped somewhere and refining costs just add a fixed amount since the cost of refining is pretty much the same everywhere.
An individual producer’s cost of production has no bearing on price except to the extent that it affects global production. Don’t think that the Norwegians can’t charge more for North Sea oil than the Americans charge for Gulf of Mexico oil just because it was harder for the Norwegians to get their oil out of the ground.
Compare oil with another globally traded commodity, gold. The price of gold is pretty much the same all over the world. You don’t expect to find bargains in gold in Irian Jaya/Papua just because the Grasberg mine is there. You don’t expect to pay extra for it in Switzerland because they have to import all of theirs.
The price of gasoline/petrol at retail is mainly determined by the global price, local supply, and TAXES. Look at the U.S. Where is the cheapest gas in the U.S.? Georgia. How much oil does the Peach State produce? None. California, on the other hand, produces oil but has among the highest prices at the pump.
As for “the hassle of international shipping [and import/export taxes]” because of “the relatively small size of European countries”: the last time I crossed a border between two European Union countries there wasn’t one.