$4 a gallon doesn't sound much for Europeans.

However if we had three times higher prices since 2002 today, as the chart shows for the US, that would mean 3,60 Euros a litre (more than $10/gallon).

Yes
In sweden the gasoline price since 2002 has not jumped much at all. The price as i recall it 2002 was about 10 krona/litre, summer 2006 it was breafly 12 krona/litre. Today when i filled my car it was 11,88 krona/litre. So the price rise here is propably not much more than the usual inflation. Gasoline is still cheap.

The price rise in USA must mostly be dependent of the decent of the USD value since 2002.