Commodity index investors, who have been widely blamed for record oil prices, sold $39bn (€28bn) worth of oil futures between the peak of the market in July and September 2, causing crude oil prices to plunge, according to a report released yesterday.

The analysis by Michael Masters, president of the Masters Capital Management hedge fund, blames such investors for driving prices to record highs and for their subsequent drop.

It comes a day before the US Commodity Futures Trading Commission is set to discuss its own study of energy trading with a congressional committee.

"I don't think it's just coincidence that the money came out after the pressure was put on these folks," said Mr Masters, who wants legislation that would set limits on index commodity holdings.

The International Energy Agency (IEA) forecast yesterday that oil demand was set to drop, which may further depress prices.

The producers' cartel OPEC called on members to stick to their agreed quotas to help maintain prices.

Crude oil futures surged to a record $147.27 on July 11, an increase of 53pc for the year, then fell 26pc to $109.71 on September 2. Oil fell $1.24 to $102.02 yesterday.

"The speculators that drove prices up basically deflated the bubble," said Fadel Gheit, director of oil and gas research at Oppenheimer & Co in New York. "They said, 'That's it, the game is over. We are going to bet on another horse.' "

JPMorgan Chase, Goldman Sachs Group, Barclays and Morgan Stanley control 70pc of the commodities swaps positions, and swaps dealers are the largest holders of Nymex crude oil futures contracts, Mr Masters said.

"These large financial players have become the primary source of the recent dramatic and damaging price volatility," he said in the report.

The IEA said world oil demand would grow by less than expected this year and next due to high prices and weaker economic conditions.

"High prices are having an impact on demand," said David Fyfe, of the IEA. "The OECD countries are feeling the impact."