Most recently, Israel’s attack on Lebanon has led to fears that it could destabilize the entire region (which was already rather unstable). Some people fear that Iran and/or Syria will take action against Israel, and Iran is a major oil producer. Iran has made threats of doing just that. Some have also talked about the possibility that Iran might withhold oil as a sign of solidarity with Hezbollah (personally I find this unlikely, considering the amount of money which Iran makes off of oil exports, but the fundamentalist regimes do not always behave logically).