Theories are often proven by elucidating predictions, then observing whether or not the predictions correspond with reality. Peak oil is supported by many well connected and level headed people in the oil industry - and exponentially increasing prices is its major prediction (diminishing supply + inelastic (and growing) demand = (wildly) increasing prices). Seems to be happening. Now if we watch total production figures, and see that they have leveled off this year, and trend down next year, well, that's sufficient to alarm me.
So what have you got? A conspiracy of oil sheiks moving the price up cause they are greedy? Too much speculation? George Soros? GWB?