(Bloomberg News) A JPMorgan Chase & Co. trader of derivatives linked to the financial health of corporations has amassed positions so large that he's driving price moves in the $10 trillion market, traders outside the firm said.

The trader is London-based Bruno Iksil, according to five counterparts at hedge funds and rival banks who requested anonymity because they're not authorized to discuss the transactions. He specializes in credit-derivative indexes, a market that during the past decade has overtaken corporate bonds to become the biggest forum for investors betting on the likelihood of company defaults.

Investors complain that Iksil's trades may be distorting prices, affecting bondholders who use the instruments to hedge hundreds of billions of dollars of fixed-income holdings. Analysts and economists also use the indexes to help gauge perceptions of risk in credit markets.

Though Iksil reveals little to other traders about his own positions, they say they've taken the opposite side of transactions and that his orders are the biggest they've encountered. Two hedge-fund traders said they have seen unusually large price swings when they were told by dealers that Iksil was in the market.

Joe Evangelisti, a spokesman for New York-based JPMorgan, declined to comment on Iksil's specific transactions. Iksil didn't respond to phone messages and e-mails seeking comment.

The credit indexes are linked to the default risk on a group of at least 100 companies. The newest and most-active index of investment-grade credit rose the most in almost four months yesterday.

The Markit CDX North America Investment Grade Index of credit-default swaps Series 18 climbed 4.4 basis points to a mid-price of 97 basis points at 5:13 p.m. in New York. The price of the index is quoted in yield spreads, which rise along with the perceived likelihood of increased corporate defaults.

A credit-default swap is a financial instrument that investors use to hedge against losses on corporate debt or to speculate on a company's creditworthiness.

Iksil may have "broken" some credit indexes -- Wall Street lingo for creating a disparity between the price of the index and the average price of the credit-default swaps on the individual companies, the people said. The persistence of the price differential has frustrated some hedge funds that had bet the gap would close, the people said.

Some traders have added positions in a bet that Iksil eventually will liquidate some holdings, moving prices in their favor, the people said.

Iksil, unlike JPMorgan traders who buy and sell securities on behalf of customers, works in the chief investment office. The unit is affiliated with the bank's treasury, helping to control market risks and investing excess funds, according to the lender's annual report.

"The chief investment office is responsible for managing and hedging the firm's foreign-exchange, interest-rate and other structural risks," Evangelisti said. It's "focused on managing the long-term structural assets and liabilities of the firm and is not focused on short-term profits."

Iksil probably traded under close supervision at JPMorgan, said Paul Miller, an analyst at FBR Capital Markets in Arlington, Virginia.

"The issue is how much capital they're putting at risk," said Miller, a former examiner for the Federal Reserve Bank of Philadelphia.

A U.S. curb on proprietary trading at banks, meant to reduce the odds they'll make risky investments with their own capital, is supposed to take effect in July. Regulators are still determining how the so-called Volcker rule will make exceptions for instances where firms are hedging to curtail risk in their lending and trading businesses.

Wall Street banks including JPMorgan, Goldman Sachs Group Inc. and Morgan Stanley have submitted comment letters and met with regulators to discuss their complaints about the rule.

"Several agencies claiming jurisdiction over the Volcker rule have proposed regulations of mind-numbing complexity," JPMorgan Chief Executive Officer Jamie Dimon said in his annual letter to shareholders released this week. "Even senior regulators now recognize that the current proposed rules are unworkable and will be impossible to implement."

JPMorgan had $4.14 billion of combined revenue last year from the chief investment office, treasury and private-equity investments, according to the annual report. The treasury and chief investment office held a combined $355.6 billion of investment securities as of December 2011, up 14 percent from a year earlier, according to a year-end earnings statement.

Chief Investment Officer Ina Drew, who runs the unit, was among JPMorgan's highest-paid executives in 2011, earning $14 million, a 6.8 percent pay cut from 2010, the bank said in a regulatory filing this week. Drew referred a request for comment to Evangelisti.

Iksil joined JPMorgan in 2005, according to his record with the U.K. Financial Services Authority. He worked at the French investment bank Natixis from 1999 to 2003, according to data compiled by Bloomberg.

The trader may have built a $100 billion position in contracts on Series 9 of the Markit CDX North America Investment Grade Index, according to the people, who said they based their estimates on the trades and price movements they witnessed as well as their understanding of the size and structure of the markets.

The positions, by the bank's calculations, amount to tens of billions of dollars and were built with the knowledge of Iksil's superiors, a person familiar with the firm's view said.