Aug. 19--The Chicago Mercantile Exchange and Chicago Board of Trade once helped the wheat stackers and hog butchers price their work.

Now those 19th Century institutions will shoulder even more of the global economy's weight, after shareholders of their parent company, CME Group, on Monday approved a deal to buy the New York Mercantile Exchange for $8.2 billion.

With this latest merger, the agricultural roots of the Chicago markets will have blossomed to include almost every aspect of commerce. Futures contracts influencing how we drive (crude oil), heat our homes (natural gas) and express our wealth (gold) will join offerings that can affect our ability to borrow money (government bonds) and buy overseas goods (foreign currencies).

The deal withstood a recent plunge in CME Group stock--which sliced about $3.3 billion from the merger price--and resistance from Nymex members, who sought more money. But CME Group needed to close the deal in order to be the exchange of choice for computerized traders who are spread across continents.

"The users today are not just in New York or Chicago, they're truly international," said CME Group Chairman Terry Duffy. "For us to expand into this asset class of energy is extremely important."

Acquiring the Nymex will bring a diverse mix of products into the CME Group portfolio, buffering the company against the recent volume drop in trading interest rate futures.

The merger also will provide access to the next financial outpost: over-the-counter contracts that are traded independent of an exchange. The Nymex already has a foothold in this space with its ClearPort system for clearing OTC energy contracts.

The risk management skills developed through ClearPort will be helpful as CME Group attempts to break into the OTC credit and interest rate markets, said CME Group Chief Executive Craig Donohue.

At an industry conference earlier this year, the German-Swiss partnership Eurex and NYSE Euronext-owned Liffe identified the clearing of OTC credit default swaps as the next great opportunity for the exchange industry.

"All of the derivatives exchanges in the world, not just here in the U.S., are trying to get the OTC market because it's about five times bigger than the exchange-trade derivatives market," said Michael Henry, an analyst for the consultant Accenture.

Through the merger, CME Group will pick up stakes in the Norwegian futures market Imarex and the recently established Green Exchange, which trades sulfur dioxide and carbon emission credits.