The two exchanges struck a deal in February to create the world's No. 1 exchange operator, trading in almost every asset class and with operations on both sides of the Atlantic.
Deutsche Boerse AG and NYSE Euronext confirm that they have today formally notified their planned business combination to the European Commission's Directorate-General for Competition, the exchanges said in a statement.
The European Commission said the preliminary review would take until August 4. This phase 1 review takes 25 working days and may be extended by 10 days if the companies offer concessions to ease any competition concerns.
The regulator can open an in-depth investigation lasting for up to 90 additional working days and can further extend this for another 15 days.
The review is expected to take five months or more, with the spotlight on the merged group's dominance in European listed derivatives and potentially strong position in European clearing.
Together, Deutsche Boerse's Eurex platform and NYSE Euronext's Liffe exchange control more than 90 percent of European listed futures trading, according to data from the World Federation of Exchanges.
Still, the fact that the exchanges have been informally talking to the European regulator about the deal in the last four months could work in their favor, said Luc Gyselen, a partner at law firm Arnold & Porter and a former senior Commission official in charge of financial services.
The long pre-notification period will have enabled the Commission to get a deeper understanding of the issues in light of the facts at hand, he said.
The EU team handling the case is led by 38-year-old Briton Nicholas Banasevic, a rising star in the European Commission who made a name for himself while working on the Microsoft
EU Competition Commissioner Joaquin Almunia said in March he expected to take a long, hard look at the takeover, as it was a complex case.
He has also stressed the risks of a one-stop shop business model, saying he preferred an open system and interoperability.
Deutsche Boerse shares were up 1.9 percent to 52.16 euros by 1217 GMT, broadly in line with a 2.1 percent gain in the Stoxx Europe 600 financial services index <.SXFP>.
(Editing by Rex Merrifield and Louise Heavens)