Direct Edge claimed a record 12.9% matched market share in U.S. cash equities last month as heavy trade in Citigroup Inc. (C) shares drove more investors to the electronic trading platform.

Jersey City, N.J.-based Direct Edge reported that its average daily volume more than doubled from year-ago levels to 1.75 billion shares as overall U.S. cash equities volume rose approximately 8% over August 2008.

Much of those gains can be attributed to Citi, which has seen its shares change hands at a blistering pace in recent weeks as investors seek hedging opportunities among cheaply priced financial stocks.

In an interview, Direct Edge Chief Executive William O'Brien acknowledged that his platform has benefited from the activity in highly traded stocks like Citigroup's; he also noted ramped up volume in CIT Group Inc. (CIT) and Fannie Mae (FNM).

But O'Brien said the trend "doesn't necessarily" favor Direct Edge over rivals BATS Exchange, NYSE Euronext (NYX) and Nasdaq OMX (NDAQ), and that the platform continues to draw more clientele, particularly from the retail sector.

Kansas City, Mo.-based BATS reported Tuesday an overall matched market share of 10% in U.S. cash equities for August.

BATS has sharpened its focus on European equities, this month launching a pricing scheme designed to lure equity investors away from the London Stock Exchange. On Sept. 1, the BATS Europe platform claimed 6% of the trading volume in FTSE 100 securities, up from 4.1% for the month of August.

Electronic upstarts Direct Edge and BATS have steadily taken market share from incumbent exchanges; for Nasdaq-listed stocks, Direct Edge surpassed NYSE Euronext (NYX) in August.

Direct Edge is now seen holding another advantage over rivals: as of Tuesday, it is the only major U.S. cash equities venue still offering flash order types, after Nasdaq OMX and BATS voluntarily dropped their versions amid controversy over the practice.

In flash orders, after a stock order has been checked against a market's main order book, it is "flashed" to a select group of participants who can act on the order before it is routed to other exchanges to be filled.

The perception that flash orders give certain market participants an unfair advantage over others has drawn scrutiny from lawmakers and the Securities and Exchange Commission, which is examining the practice.

Officials at Direct Edge, which is pursuing exchange status with the SEC, have said that flash orders represent only about 5% to 6% of matched volume on the platform.

However, the profitability of the practice is seen helping Direct Edge lower its overall trading fees.

-By Jacob Bunge, Dow Jones Newswires; (312) 750 4117; jacob.bunge@dowjones.com; and Joan E. Solsman, Dow Jones Newswires; 212-416-2291; joan.solsman@dowjones.com

(Geoffrey Rogow contributed to this report.)