CME Group Inc. (CME) reclaimed its spot as the world's largest derivatives exchange last month, reporting trading volume Thursday that topped that of rival Eurex.

Activity in CME's core interest-rate-futures products rose 8% from May to June as investors saw signs of improvement in the economic climate, fueling the busiest trading day this year for the Chicago-based exchange operator.

But overall volume remained well below year-ago levels at both CME and Eurex, and CME also saw its average rate per contract decline for the fourth consecutive month.

A total of 251 million contracts changed hands in June on CME's markets, which include the Nymex energy platform.

Eurex, which reported June data on Wednesday, traded 232.5 million contracts, including the contribution from the International Securities Exchange options platform.

Total volume remains 17% lower year-on-year at Eurex, co-owned by Deutsche Boerse AG (DB1.XE) and SWX Swiss Exchange, and 20% lower for CME.

CME shares were 1.6% lower in early trade at $303.49, while Deutsche Boerse shares were also down at 52.01 euros.

CME on Thursday also reported another drop in its average rate per contract, which fell to $0.812 for the three-month period ended in May.

Its average fees have fallen nearly 6 cents since January, when the exchange operator suffered its first rate-per-contract, or RPC, decline in more than a year.

CME collects the majority of its fees from interest-rate futures, but that activity has sagged as the Federal Reserve lowered its benchmark rate to near zero.

Equity-index products, which carry a higher rate per contract, have seen increased activity, thanks to stock-market volatility, but not enough to make up the difference.

Interest-rate trading fell 24% from year-ago levels in June, but posted its best 2009 performance, averaging 5.1 million contracts per day.

On June 5, CME reported its busiest day ever in eurodollar futures, as a little more than six million contracts changed hands after the release of a surprising monthly employment report.

But average daily volume for Treasury futures and options was 35% below June 2008 totals, while eurodollar futures sustained a 16% drop. The daily volume average for federal-funds products fell 49%.

Rate-futures trading activity at Eurex was nearly one-third lower than year-ago levels, though June volume rose about 30% from May.

Equity-index derivatives far outpaced Eurex's other product groups, with 71.1 million contracts traded last month, though levels remained 17% below June 2008. At CME, volume in equity-focused products was about 21% lower year-on-year.

Atlanta-based IntercontinentalExchange Inc. (ICE) reported a record average daily volume of 1.1 million contracts in June, a 14% year-on-year increase as energy traders hedged against shifts in the price of crude oil.

Nymex, which trades the benchmark West Texas Intermediate crude-oil contract, reported overall volume down 4% from year-ago levels, with its ClearPort over-the-counter platform registering a 33% bump in activity.

ICE also reported that its ICE Trust credit derivatives platform had cleared $1.3 trillion in notional contract value since its March launch.

Shares in ICE were slightly higher in midmorning trade, at $111.91.

-By Jacob Bunge, Dow Jones Newswires; 312-750-4117; jacob.bunge@dowjones.com

-By Howard Packowitz, Dow Jones Newswires; 312-750-4132; howard.packowitz@dowjones.com