In the last half hour of trading Friday, Anadarko Petroleum briefly declined from more than $90 a share to as low as one penny before rebounding above its original price. NYSE Euronext busted all trades below $87.56. The trades were not automatically stopped by newly implemented limit-up/limit-down regulations because the rules will not be expanded to cover the last half hour of trading until after Aug. 1, according to the Securities and Exchange Commission.

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