It's reasonable to conclude that speculators are also playing a key role in the current oil-price run-up, in addition to the sabre-rattling over Iran and other geopolitical and economic factors. A study by none other than Goldman Sachs has found that each million barrels' worth of speculation adds 10 cents to every barrel of oil. There were about 233.9 million crude oil contracts that were the subject of speculation as of Feb. 28. Thus speculation added $23.39 to the price of a $108 barrel of oil, which translates to 56 cents a gallon at the pump. Without speculation, Forbes writer Bob Lenzner notes, a barrel of oil would have cost as little as $74.61, and the cost of fuel would have been $3.12 a gallon on Feb. 28, and not the price it was actually commanding in the northeastern U.S.: $3.68.

http://www.salon.com/2012/03/07/the_real_way_to_hold_down_gas_prices/singleton/?mobile.html