This note from The Economist explains much of the recent rise in oil prices:

THE oil market is behaving like a bucking bronco again, and politicians are once more blaming speculators for careening prices. It is difficult to assemble a definitive explanation for the rally: a weak dollar helps oil prices, but evidence for improving supply and demand remains thin. Positions held on NYMEX, the New York commodities exchange, have indeed soared. In 2008 America’s Commodity Futures Trading Commission (CFTC), which regulates NYMEX, examined how the changing positions of hedge funds affect prices. It found correlation, not causation, but its investigations were hampered by the fact that it could not examine intra-day trades. Nor could it monitor certain derivatives, such as those traded via London’s InterContinental Exchange (ICE), in which Wall Street dealers are particularly prominent. But in a sign of things to come in the oil market, on June 12th the CFTC said it had launched a public investigation to see whether the biggest natural-gas contract traded on ICE was moving prices around in the more regulated futures markets.