The Chicago Mercantile Exchange has effectively rolled its tank onto the lawns of Europe's two biggest derivatives exchanges. But its arrival isn't likely to have an immediate impact.

Six months ago, European regulators blocked the merger of Deutsche Börse, which owns Eurex, and NYSE Euronext, which owns Liffe, on grounds the combination would have eliminated competition in the trading of interest-rate derivatives, with a combined 95% share, and harmed the European economy. A raft of exchanges and brokers have since taken advantage, announcing plans for European derivatives trading, including Nasdaq OMX Group, the London Stock Exchange Group and interdealer broker ICAP. CME Group, the latest, looks to be joining the charge.