Actually that is part of the problem, the US has been building up the Strategic Oil Reserve. They are going from around 750million to a billion or so barrels.
There are many factors I have seen reported:
1. Declining Dollar. Oil prices are in dollars, so as the dollar declines OPEC wants more dollars to maintain their buying power.
2. World coming out of recession driving up demand
3. New EPA regulations (Big one here). US regulations are getting so tight that other countries do not bother trying to meet them so we cannot import refined gasoline. US refiners are not adding capacity since it is getting impossible to do with regulations.
So, we have increased global demand for the raw product, our currency is devaluing driving up the price of the raw product... this combined with the ever increasing clean air regulations for producing gasoline, has resulted in a double squeeze on the price/supply in the US.