3. The main reason is not supply and demand. It's US manipulating the oil price by oil reserve and future contract.

(1) Quote, "The former Fed chief also detailed how investors, rather than users of oil, have come to set the price of oil through purchasing futures contracts." Though Greespan use "investors" instead of "speculators".

(2) From supply side:

08-03-05. OPEC to maintain current production; blames US for economic ’mismanagement’
Published: Wednesday, March 5, 2008 | 3:03 PM ET
Canadian Press: William Kole, THE ASSOCIATED PRESS

OPEC President Chakib Khelil told reporters the global market is being affected by what he called "the mismanagement of the U.S. economy," and that America's problems were a key factor in the cartel's decision to hold off on any action.

"If the prices are high, definitely they are not due to a lack of crude. They are due to what's happening in the U.S.," Khelil said. "There is sufficient supply. There's plenty of oil there."

Though Khelil uses "US economy" instead of "speculators".

(3) From demand side:

Quote, "Shell CEO says record oil not due to shortage
Thu May 22, 2008 5:24pm BST
Shell CEO says record oil not due to shortage | Markets | Reuters

(4) What US Senate Committee found:

Quote, "The real reason why oil prices are rising

June 02, 2008
...........
The finding of US Senate Committee in 2006
In June 2006, when the oil price in the futures markets was about $60 a barrel, a Senate Committee in the US probed the role of market speculation in oil and gas prices. The report points out that large purchase of crude oil futures contracts by speculators has, in effect, created additional demand for oil and in the process driven up the future prices of oil.......
The report further estimated that speculative purchases of oil futures had added as much as $20-25 per barrel to the then prevailing price of $60 per barrel. In today's prices of approximately $130 per barrel, this means that approximately $100 per barrel could be attributed to speculation!...

*What is interesting to note is that the US strategic oil reserves were at approximately 350 million barrels for a decade till 2006. However, for the past year and a half these reserves have doubled to more than 700 million barrels. Naturally, this build-up of strategic oil reserves by the US (of 350 million barrels) is adding enormous pressure on the oil demand and consequently its prices.

The real reason why oil prices are rising