Ironically, this development grew in part out of worries during the height of the financial crisis in 2008. A major concern during the meltdown was that no one — not even government regulators — fully understood the size and interconnections of the derivatives market, especially the market in credit default swaps, which insure against defaults of companies or mortgages bonds. The panic led to the need to bail out the American International Group, for instance, which had C.D.S. contracts with many large banks.

In the midst of the turmoil, regulators ordered banks to speed up plans — long in the making — to set up a clearinghouse to handle derivatives trading. The intent was to reduce risk and increase stability in the market.

Two established exchanges that trade commodities and futures, the InterContinentalExchange, or ICE, and the Chicago Mercantile Exchange, set up clearinghouses, and, so did Nasdaq.

Each of these new clearinghouses had to persuade big banks to join their efforts, and they doled out membership on their risk committees, which is where trading rules are written, as an incentive.

None of the three clearinghouses would divulge the members of their risk committees when asked by a reporter. But two people with direct knowledge of ICE’s committee said the bank members are: Thomas J. Benison of JPMorgan Chase & Company; James J. Hill of Morgan Stanley;Athanassios Diplas of Deutsche Bank; Paul Hamill of UBS ; Paul Mitrokostas of Barclays ;Andy Hubbard of Credit Suisse; Oliver Frankel of Goldman Sachs; Ali Balali of Bank of America; and Biswarup Chatterjee of Citigroup.

Through representatives, these bankers declined to discuss the committee or the derivatives market. Some of the spokesmen noted that the bankers have expertise that helps the clearinghouse.

Many of these same people hold influential positions at other clearinghouses, or on committees at the powerful International Swaps and Derivatives Association, which helps govern the market.

Critics have called these banks the “derivatives dealers club,” and they warn that the club is unlikely to give up ground easily.

“The revenue these dealers make on derivatives is very large and so the incentive they have to protect those revenues is extremely large,” said Darrell Duffie, a professor at the Graduate School of Business at Stanford University, who studied the derivatives market earlier this year with Federal Reserve researchers. “It will be hard for the dealers to keep their market share if everybody who can prove their creditworthiness is allowed into the clearinghouses. So they are making arguments that others shouldn’t be allowed in.”

Perhaps no business in finance is as profitable today as derivatives. Not making loans. Not offering credit cards. Not advising on mergers and acquisitions. Not managing money for the wealthy.

The precise amount that banks make trading derivatives isn’t known, but there is anecdotal evidence of their profitability. Former bank traders who spoke on condition of anonymity because of confidentiality agreements with their former employers said their banks typically earned $25,000 for providing $25 million of insurance against the risk that a corporation might default on its debt via the swaps market. These traders turn over millions of dollars in these trades every day, and credit default swaps are just one of many kinds of derivatives.

The secrecy surrounding derivatives trading is a key factor enabling banks to make such large profits.

If an investor trades shares of Google or Coca-Cola or any other company on a stock exchange, the price — and the commission, or fee — are known. Electronic trading has made this information available to anyone with a computer, while also increasing competition — and sharply lowering the cost of trading. Even corporate bonds have become more transparent recently. Trading costs dropped there almost immediately after prices became more visible in 2002.

Not so with derivatives. For many, there is no central exchange, like the New York Stock Exchange or Nasdaq, where the prices of derivatives are listed. Instead, when a company or an investor wants to buy a derivative contract for, say, oil or wheat or securitized mortgages, an order is placed with a trader at a bank. The trader matches that order with someone selling the same type of derivative.

Banks explain that many derivatives trades have to work this way because they are often customized, unlike shares of stock. One share of Google is the same as any other. But the terms of an oil derivatives contract can vary greatly.

And the profits on most derivatives are masked. In most cases, buyers are told only what they have to pay for the derivative contract, say $25 million. That amount is more than the seller gets, but how much more — $5,000, $25,000 or $50,000 more — is unknown. That’s because the seller also is told only the amount he will receive. The difference between the two is the bank’s fee and profit. So, the bigger the difference, the better for the bank — and the worse for the customers.

It would be like a real estate agent selling a house, but the buyer knowing only what he paid and the seller knowing only what he received. The agent would pocket the difference as his fee, rather than disclose it. Moreover, only the real estate agent — and neither buyer nor seller — would have easy access to the prices paid recently for other homes on the same block.