Fidelity and other major U.S. financial services firms, including Goldman Sachs Group Inc and Credit Suisse Securities USA LLC, have made BATS a leading exchange for stocks and equity options by using it to execute increasing amounts of their customers' trades for companies listed on major exchanges such as the New York Stock Exchange and Nasdaq.

Fidelity, Goldman and other companies can choose from a number of other venues should BATS continue to falter, including the other exchanges themselves. They are also not obligated to keep using BATS.

The BATS exchange suffered a disastrous software problem on Friday, the day BATS' shares made their debut on its own exchange.

The glitch caused its new stock to plummet to near zero value, and triggered a brief halt in the trading of Apple Inc shares on its exchange.

Later on Friday, BATS took the rare decision to withdraw its initial public offering.

BATS' fast, all-electronic execution has attracted more volume and customers in recent years, making BATS more diversified. It handles about 11 percent of U.S. equity trading, and expanded in Europe late last year with the acquisition of an alternative trading platform known as Chi-X.

Boston-based Fidelity's National Financial Services unit used BATS to execute up to 11 percent of its customer orders in the fourth quarter, according to the latest disclosures to U.S. regulators. National Financial represents Fidelity and about 300 client firms with about $365 billion in assets under administration.

But on Sunday, Fidelity would not say whether it would continue to use BATS.

"Fidelity has many venues available to our traders, so this will have no effect on us. We monitor the connections to, and the performance of, all trading systems that we interact with," the mutual fund company said in a statement.

BATS, in disclosures made before its IPO, said "no member is contractually or otherwise obligated to continue to use the company's services."

During the fourth quarter, National Financial said BATS ranked No. 4, handling 9.73 percent of its non-directed customer orders for securities listed on the New York Stock Exchange.

A non-directed order allows the broker to choose the exchange for executing a trade on behalf of the customer. About 99 percent of National Financial's orders are non-directed, filings show.

BATS also received about 11 percent of National Financial's customer orders for securities listed on Nasdaq. That put BATS at No. 3, behind National Financial, which handled 33 percent of its customer orders, and Nasdaq, which handled about 19 percent.

In contrast, Fidelity's arch rival, Vanguard Group, showed no exposure to the BATS exchange in the fourth quarter. Vanguard Brokerage Services did not list BATS as a major venue for executing customers trades.

Goldman Sachs reported that BATS handled 6.1 percent of its non-directed customer orders for NYSE-listed securities and 7.7 percent for Nasdaq-listed securities, according to fourth-quarter disclosures relating to orders of less than $200,000.

But Goldman also uses the services of a rival exchange Direct EDGE Holdings LLC, in which it has an indirect ownership interest. In addition, Goldman uses Sigma X, an alternative trading system owned and operated by a Goldman affiliate, according to U.S. regulatory filings.

Goldman was not able to immediately comment on Sunday.

Credit Suisse, which declined to comment, used BATS in the fourth quarter for 11 percent of non-directed customer orders for NYSE-listed securities, filings show.

During 2011, BATS said one undisclosed member received about 13 percent of its liquidity payments. In the fourth quarter, Fidelity's National Financial, for example, received an average payment of $0.0025 per share for each order it routed to BATS that created liquidity for its exchange.

In 2009, BATS paid one member about 51 percent of the company's liquidity payments, according to its IPO disclosures. No other BATS' members accounted for more than 10 percent of the company's liquidity payments in each of the past three years, according to U.S. regulatory filings.

(Reporting By Tim McLaughlin, Editing by Alwyn Scott, Desking by G Crosse)

By Tim McLaughlin