I think what you're really hitting at is whether speculation in the futures market can affect the price in the spot market. It absolutely can. While the futures market is a zero sum game (somebody has to go long and somebody has to go short for the same amount, short sells the contract to the buyer/long), the price of oil at a futures price can effectively come back to influence the spot. Say, for example, we have a new futures price of $140 for delivery in August 2011. This gives us an expectation of what oil MAY be in August, according to the "market", but oil is at $100 right now. That means in 3 months somebody thinks oil is going to $140.
What happens if, because of that "expectation", somebody puts a new price target for oil to hit $140 by august, say Goldman. That means that people say "oohh wow, oil is going to $140 by august, I need to get in on the action". That also means that people will be willing to buy the oil now at $100 and store it, provided storage costs less than $40/bbl during the holding period. Now, you'd see oil inventories going up in this case, in 2008 there were many oil ships off coasts holding oil. In other cases you heard/saw tanks being full.
Now, what happens if nobody is collecting physical but the expecation is that spot will hit $140 by August. The futures pricing takes into account time-value, margin requirements and the fact you don't have to store anything, thus, once you subtract those out, that's what spot should be. What happens if there's a lot of conviction in the futures, say, tons of money flowing into futures? The stronger the conviction, the more the physical market can react to the conviction. Why sell oil now for $100 when it's actually worth $140 - TVM - storage - margin costs = $135.
So the new spot for oil should be $135. As others have mentioned, these futures offer huge leverage opportunities, you only need a small amount of capital to get a big contract.
Obviously people say that futures do not create spot demand and cannot influence the price of the supply/demand of the spot, but I disagree.
It doesn't help when people trumpet $200 oil, like T. Boone Pickens.