A trader signals near the S&P 500 futures pit at the CME Group in Chicago near the close of trading, Thursday, May 6, 2010. CME’s equity index futures markets figured heavily into early theories as to the cause of that day’s stock market panic. (AP Photo/Kiichiro Sato)

Dow Jones Newswires | CME Group Inc. will join other market operators appearing before
Congress Tuesday as lawmakers seek answers as to what sparked a massive
rout in stock and futures markets last Thursday.

Representatives from the world’s largest futures exchange operator will
head to Capitol Hill to appear alongside NYSE Euronext and Nasdaq
OMX Group Inc. after a summons last Friday by House Financial
Services Capital Markets Subcommittee Chairman Paul Kanjorski (D, Pa.).

A range of theories and a blurry picture of trading activity has emerged following the breathtaking price volatility that rocked financial markets May 6, with electronic trading systems seen playing a central role.

The Dow Jones Industrial Average lost about 1,000 points and triggered emergency measures by exchanges before stocks staged a partial recovery.

CME’s equity index futures markets — in particular electronically traded contracts tied to the S&P 500 — figured heavily into early theories as to the cause of the sell-off, with market participants blaming an erroneous trade in the market as the starting point.

That theory has since been discarded after CME noted that neither it nor its customers reported technical glitches that might have sparked such a massive market move. In an unusual move, the exchange also said Citigroup Inc. — the subject of speculation over a possible erroneous trade — hadn’t been the subject of any unusual activity.

Officials at the exchange have also pointed to a series of risk-control measures in place to guard against any such massively erroneous trade.