It's Bush's fault
Have you noticed that when the gas prices go up, some folks immediately start blaming the president? However, when gas prices go down, you don't here a word?
I'm no economist, but I suspect the prices have a lot more to do with supply and demand, rather than anything else. If somebody with a lot of money to spend tries to buy up a lot of oil, (as I understand China has been doing recently), or the amount of oil available for purchase decreases, prices will go up.
If more oil becomes available, or if the demand decreases, prices go down. That's how it works.
It even works that way on Ebay.