its not any single 1 cause. Its a number of reasons.

Speculation = 30-40 dollars of the rise

dollar value = increased oil cost

supply and demand = increased oil cost

Speculation is easily the cause for 30-40 dollars extra cost on the price of a barrel of oil. Its also the easiest and quickest fix while the economy and industry have time to adjust.

There is a problem when even the Saudis are saying the price of a barrel of oil is over inflated.