Politics perhaps. That is if you consider OPEC moves to be political.
The speculation angle is nonsense. It reflects a fundamental misunderstanding of the long term macro price movement.
And "overpriced" is a word that is defined by each person based on their opinion or whether they are a buyer or seller of oil.
People will only pay what it is worth to them. Sellers will always get the highest price possible. It's not that hard.
Since I'm a BUYER of oil, it is grossly overpriced. The increase in consumption in the last couple of years worldwide has not even outstripped the increase in supply. Speculation is rampant. Oh,,,,could Iran cause more trouble. Oh,,,,will OPEC cut production to keep prices high. Oh,,,,will ANWR be opened to drilling. Oh,,,,,will the hurricane season wipe Louisiana off the map due to global warming. It goes on and on.
http://www.gasandoil.com/goc/features/fex53581.htm