Why are jet fuel prices very similar in North America and Europe, yet automotive fuel prices are very different?
Jet fuel for international commercial aviation is effectively not taxed due to an agreement between ICAO member states. (See here ICAO PDF  ). Therefore the prices closely track to cost of production and distribution. These are similar worldwide. Differences exists due to local taxes on companies, difference in costs of transport, effects of competition on price etc, but these effects are limited. 

Automotive fuel is taxed. I am originally from the Netherlands, where we have one of the highest taxes in the world when it comes to fuel taxes. Petrol costs at the moment approximately 1.66 Euro/litre, of which 68.84% is taxes. 

In the US, the average total tax (federal plus local) is \$0.4818 on a gallon of gas (equivalent to \$0.1289 per litre).

So the difference in tax makes most of the difference in automotive fuel prices.

Sources: wikipedia