http://en.wikipedia.org/wiki/Opec#Responding_to_war_and_low_prices
esentially OPEC trading in the us dollar for many years, has kept our gas prices lower than the rest of the world. When other countries (venezuala & iran) began deciding to trade thier oil in the euro market, after we invaded iraq, other members of opec began talking about shifting all of thier trading into euro, along with them. Once that happened, fear drove our market cost up.