An upstart competitor is buying the venerable New York Stock Exchange, long the symbol of robust American capitalism.

The owner of the 220-year-old New York exchange, NYSE Euronext, said Thursday it has agreed to an $8.2 billion deal to sell the iconic Wall Street fixture to IntercontinentalExchange. The 12-year-old Atlanta-based bourse focuses on trading future energy and commodity securities, while the New York exchange has long been the stock trading home to the biggest and best known American companies.

The deal marks the revival of stock exchange mergers, assuming U.S. and European regulators approve it. Last year, regulators scuttled two attempts by the New York exchange to sell itself, to Deutsche Borse, and later to a combined bid from the IntercontinentalExchange and Nasdaq exchanges.

The sale of the New York exchange is in part a reflection of the changed nature of securities trading. Wall Street's share of stock trading dropped from 82 percent to 21 percent over recent years as new exchanges sprung up around the world and more complex financial instruments were offered for sale to the world's wealthiest investors.

NYSE Euronext also owns the biggest French and Dutch exchanges. As a result, the merged exchange would create the biggest trans-Atlantic trading house for stocks and derivatives, securities whose value are determined by underlying assets.

The New York Stock Exchange had a humbler beginning. It was formed by 24 stockbrokers under a buttonwood tree on Wall Street in 1792.