CHICAGO (Reuters) - NYSE Euronext <NYX.N> and Germany's Deutsche Boerse AG <DB1Gn.DE> will become the market leader of the ultra-competitive U.S. options trading industry once their merger is complete, data from clearinghouse OCC showed on Monday.

Last month NYSE and Deutsche Boerse shareholders approved the transatlantic merger, which will bring together not only Europe's two biggest derivatives exchanges but also three mid-ranking U.S. options marketplaces.

The exchanges -- Deutsche Boerse's International Securities Exchange and NYSE's Amex and NYSE Arca venues -- together handled 40.3 percent of all U.S. stock- and stock-index options trades last month, according to figures on the OCC website.

Bragging rights for the No. 1 spot have in recent months gone to either CBOE Holdings Inc <CBOE.O>, which owns the oldest U.S. options exchange, or Nasdaq OMX Group <NDAQ.O>, which operates two venues, PHLX and NOM.

CBOE, which also owns the electronic C2 market, handled 26.2 percent of all options contracts traded in July; Nasdaq handled 25.9 percent.

Traders say they expect NYSE and Deutsche Boerse to lose some of their collective volume once they complete the merger, as market participants spread their business among competitors.

But the large lead the three exchanges have over their nearest rivals suggests they will keep their collective top spot for some time to come, analysts have said.

The merger still needs the approval of regulators, which in Europe may require a review lasting through the end of the year.

Deutsche Boerse is buying NYSE Euronext for about $9 billion.

(Reporting by Ann Saphir; Editing by Lisa Von Ahn)