"These speculators and hedge funds are high-risk gamblers who drive up energy prices to line their own pockets at the expense of others," said US Senator Richard Blumenthal, a Connecticut Democrat, in a statement he planned to deliver at a Hartford gas station Monday.

"There is strong evidence the recent surge in gas prices has little to do with the fundamental supply and demand for oil," a group of 13 US Senators, including 12 Democrats and one independent, wrote in a March 16 letter to Commodity Futures Trading Commission Chairman Gary Gensler, as $4/gallon gas returned to US pumps.  "Speculators are seizing on recent political turmoil in North Africa and the Middle East to drive energy prices to unwarranted levels."

The argument against speculators is one Democrats have been making for years.

"Make no mistake about it, the excessive speculation in commodity markets is having a devastating effect at the gas pump that is rippling through our entire economy," said then-Representative Bart Stupak, a Michigan Democrat, during a June 2008 hearing before a House Energy and Commerce subcommittee hearing he chaired.

"The reason we have oil at $130, $140, $145 a barrel - like a roman candle going up, up, up - is because we have excessive, relentless speculation in these markets," Senator Byron Dorgan, a North Dakota Democrat, told reporters in July 2008.

While the argument against speculators has stayed largely the same, the amount of publicly available market data on their activities has multiplied and the criticism of them has only amplified.

But the link between high prices and speculation remains as debatable as ever, exchange officials and government regulators said during a Futures Industry Association conference last week.

On Tuesday, CFTC commissioner Bart Chilton, a proponent of speculative position limits in commodity markets, said the sheer size of their current positions "has the potential of moving markets, of influencing true price discovery." Chilton pointed to CFTC data showing that between June 2008 and January 2011, the number of futures equivalent contracts held by speculators increased by 64%, from 617,000 to more than 1 million, but during a panel discussion at the conference on Wednesday he downplayed the perception that he was claiming speculators had caused prices to skyrocket.

"I'm not saying speculation meant higher prices [in 2008], I'm not saying speculation means $100 oil," Chilton said. "I'm not saying that."

While Chilton cited a handful of studies that he claimed show the link between speculation and high prices, the heads of CME Group, parent company of NYMEX, and IntercontinentalExchange both said there is still no evidence that such a link exists.

"You look at all the empirical evidence and research that's been done in the last three to four years and there's still not one reliable study that actually substantiates the idea that speculators are having an impact on prices," said CME CEO Craig Donohue.

"There seems to be this populist belief right now that markets are not correctly predicting prices," said Jeffrey Sprecher, chairman and CEO of ICE. "There's a sense that there are speculators, and energy prices are up, so that must be the cause and effect and without further analysis. You can't just make that leap without knowing."

The issue is a heated one right now for the CFTC, which is considering a proposal to impose federal position limits on 28 core physical delivery futures contracts, including four energy and five metals contracts, in an attempt to quell market speculation.

But the challenge of approving these limits was clear at the conference as Commissioners Michael Dunn, a Democrat, and Scott O'Malia and Jill Sommers, both Republicans, said the jump in speculators in markets was not enough evidence for them to say they were unduly influencing prices.

"If we use the example of the [agriculture] contracts, nine contracts where we have federal, hard position limits, they have not been spared from high prices or volatility," O'Malia said. "There are many other factors [in volatility], and I just haven't seen the relationship that position limits cure that."

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