A (2005) look at the worlds gas/petrol prices per US Gallon. Cheapest is Venezuela at $0.17/gallon. US is ~$2.70/gallon, UK is $6.65/gallon.

Figures from Mid 2007 show a distinct change (USD/Gallon):

United Kingdom $8.37

Ireland $5.40

Czech Republic $5.10

United States $2.88

Saudi Arabia $0.45

Venezuela $0.19

From here