Just about everyone in Washington, including Barack Obama and John McCain, has rushed to attribute the run-up in gasoline prices to evil speculators, preferring to avoid the simpler explanation of supply-and-demand, especially from rapidly-developing China and India, and to sidestep the many ways government acts to increase petroleum and gasoline prices (including collecting more in taxes than the oil companies get in profit and forbidding drilling in numerous places where we know there's avaialble oil).
After being badgered by politicians looking for a villain, the Commodity Futures Trading Commission did an in-depth study (link here leads to a link to the PDF of the full-length study), scrutinizing millions of transactions involving billions of dollars, of the role of speculators in the oil and gasoline markets that was released last week. It busts the myth completely -- especially since it contains no explanation for the recent fall in crude oil prices to around $90 a barrel, whereas reduced demand in the U.S. due to economic troubles and high prices does so rather handily. But don't expect to stop hearing it voiced.
The CFTC found that index traders and swap dealers actually reduced their stake in crude oil futures as prices spiked. More traders wewre going short than long, which had at least some impact of hiolding prices down. And commodity index funds have only 13 percent of the oil market, not the 70 percent some conspiracists were estimating.