Oil trading data that exposed the extensive positions speculators held in the run-up to record high prices in 2008 were intentionally leaked by a U.S. senator, sparking broader concern about industry confidentiality as Congress moves on Wall Street reform.

Senator Bernie Sanders, a staunch critic of oil speculators, leaked the information to a major newspaper in a move that has unsettled both regulators and Wall Street alike.

In a June 16 e-mail reviewed by Reuters, a senior policy adviser to Sanders discusses how his office received private data with the names and positions of traders and forwarded it exclusively to a Wall Street Journal reporter.

The e-mail, which also attaches two files with the data, was sent to Public Citizen's Tyson Slocum asking him to review it and speak with the newspaper about his observations.

In a statement from Sanders provided to Reuters, Sanders said he felt the data needed to be publicly aired.

The CFTC has kept this information hidden from the American public for nearly three years, he said. This is an outrage. The American people have a right to know exactly who caused gas prices to skyrocket in 2008 and who is causing them to spike today.

The leaked information has sparked concern at the Commodity Futures Trading Commission, which is legally prohibited from releasing confidential information that identifies trader positions and identities.

The leak also raises broader questions as U.S. regulators gear up to collect massive new amounts of private data from market players on everything from swaps and hedge funds to blueprints for how large financial firms can be liquidated. The breach of data could make Wall Street less reluctant to hand over sensitive information if they fear it is not appropriately safeguarded.

This type of incident will have a chilling effect on derivatives trading in the U.S. because market participants will be reluctant to take the risk that their positions will be exposed to the public-and their competitors, John Damgard, president of the Futures Industry Association, said in a statement sent to Reuters.

Republicans have already raised concerns in recent hearings about the Treasury's new Office of Financial Research created by Dodd-Frank, and whether its collection of data from hedge funds and banks may constitute a regulatory overreach.

Although the CFTC is barred from releasing confidential data, the law does require the CFTC to hand over such information if a Congressional committee acting within its proper authority requests it. Once it is in the hands of Congress, there is nothing to prevent lawmakers from releasing it publicly.

The leaked data contains long and short positions held by oil traders in 2008, the same year that oil prices spiked to $147 a barrel. Critics at the time accused oil speculators of driving up prices, leading lawmakers to later insert a provision into the Dodd-Frank Wall Street overhaul law compelling the CFTC to place stricter limits on how many commodity contracts any one trader can control.

Among the kinds of traders accused of excessive speculation included passive long investors such as pension funds, which often seek exposure to commodities markets indirectly by going through an intermediary swap dealer such as such as Goldman Sachs and Morgan Stanley.

The data that was leaked to the Wall Street Journal was compiled by the CFTC in 2008 during a special call in which the agency sought crude oil position data from swap dealers so they could piece together market activity occurring both on and off the exchange, people familiar with the matter said.

The CFTC first became aware of the breach of the data after a staffer from Sanders' office sent the agency an e-mail with the information and asked the CFTC's chief economist to discuss it more.

The agency began exploring internally whether or not any staffers were responsible for the leak, and concluded that no CFTC employees were involved, according to people familiar with the matter.

It is unclear exactly how Sanders acquired the private information, and a spokesman declined to say.

But people familiar with the matter say the data later obtained by Sanders was first formally requested by the U.S. House Energy Committee. From there it somehow migrated over to the U.S. Senate.

(Reporting by Sarah N. Lynch; Editing by Russell Blinch and Alden Bentley)