Chris Concannon, president and chief operating officer of trading firm Virtu Financial, and Jose Marques, global head of electronic trading at Deutsche Bank, are the front-runners for the position, the sources said. Neither candidate, however, is guaranteed to take the job and others remain in the mix, one of the sources said.

Concannon and Marques could not immediately be reached for comment. BATS and Deutsche Bank declined to comment.

BATS abruptly announced in July that its president, William O'Brien, had left the company less than six months after BATS merged with rival Direct Edge, where O'Brien had been chief executive. BATS CEO Joseph Ratterman took on the dual CEO/president role, which he also held from June 2007 through January 2014.

The company has been carrying out the search on it's own, rather than using a recruiting agency, one of the sources said. Both candidates have strong ties to the exchange operator, as Concannon is part of BATS' exchange board, and Marques is part of the company's investor board.

Concannon, is a former executive of Nasdaq OMX Group and once worked as an attorney for the U.S. Securities and Exchange Commission.

Marques has been global head of electronic trading at Deutsche Bank since the beginning of 2010, and previously was a managing director at Credit Suisse Group AG and chairman of LeveL ATS, a Boston-based alternative trading system, or "dark pool." Marques' relationship with BATS goes back to 2006, when Credit Suisse acquired a minority stake in the exchange operator.

The merger of BATS and Direct Edge received its final regulatory approvals in late January, creating the second-largest U.S. stock exchange, ahead of Nasdaq and just behind Intercontinental Exchange Inc's New York Stock Exchange in terms of equity trading volumes.

BATS also runs a U.S. equity options market as well as BATS Chi-X Europe, which is the largest pan-European equities exchange by market share and value traded.

(Reporting by John McCrank and Herbert Lash; Editing by Chizu Nomiyama and Andrew Hay)

By John McCrank and Herbert Lash