I like this section from the first article M had too:
The art of the deal
So just how does speculation work?
Well, investors with large sums of cash purchase, on contract, barrels of oil at a pre-determined price for a future date, anticipating that, with rising prices, they will make a profit when the oil is delivered. So, for example, speculators may purchase in 2008 a barrel of oil at a certain price because of a contract - and leverage it later to a petroleum user for a higher price.
The trick is, these speculators themselves drive up the price because, by entering the market, they drive up demand.
"The large purchases of crude oil futures contracts by speculators have, in effect, created an additional demand for oil, driving up the price of oil to be delivered in the future in the same manner that additional demand for the immediate delivery of a physical barrel of oil drives up the price on the spot market," the Senate report stated. "As far as the market is concerned, the demand for a barrel of oil that results from the purchase of a futures contract by a speculator is just as real as the demand for a barrel that results from the purchase of a futures contract by a refiner or other user of petroleum."
Even in 2006, the report stated, analysts estimated that speculative purchases of oil futures had added as much as $20-$25 per barrel to the 2006 price of crude oil, thereby pushing up the price of oil at the time from $50 to approximately $70 per barrel.
In addition to this direct effect, the report stated, speculation has a pernicious domino effect: by purchasing large numbers of futures contracts, and thereby pushing up futures prices to even higher levels than current prices, speculators have provided a financial incentive for oil companies to buy even more oil and place it in storage.
**TR: I see why you say some want to build surpluses.