An Analogy
A friend of mine plays World of Warcraft, and for a while, took over the market for a particular item in the Warcraft auction house.
Let's say it was Khorium Ore. Buddy logs in, buys up all the Khorium that's for sale for less than a certain amount, and then lists it for sale at the higher price.
Every day he does this, so that now he's effectively re-priced Khorium at the rate he has chosen.
The people mining Khorium are happy - someone is buying all the Khorium they can mine. Buddy's happy, because he's making a profit on every sale. It's everyone else on the server that's getting ripped off by his activites.
Now, substitute oil for Khorium, speculators for my buddy manipulating prices, and consumers for the people getting ripped off.
Is that what's going on? And, how does it end?
In Warcraft, it would eventually end because the supply would increase to the point where buddy couldn't possibly buy it all. But the supply of oil is limited, both artificially (by OPEC) and by the existing capacity to pull the stuff out of the ground.
Either the speculators know something that we don't - that supply is about to be naturally constrained by a real shortage - or they're creating a bubble, that will eventually collapse when supply outstrips their ability to buy it.