NEW YORK (CNN/Money) - Shares of Northwest Airlines and Delta Air Lines continued to trade on their respective stock exchanges Thursday despite the bankruptcy filings both airlines made Wednesday.

A NYSE press release said the exchange, where Delta is traded, had reviewed the situation at the airline and that the exchange had decided to allow the stock to resume trading on its floor.

NYSE said it will monitor Delta stock and immediately suspend trade if the share price become "abnormally low," if the exchange "receives authoritative advice that the security is without value," or if the company fails to meet certain capitalization requirements, including a minimum share price of over $1 for a 30 day period.

A spokesman for Nasdaq, the exchange where Northwest is traded, said it would also continue to monitor the situation, saying that a bankrupt company is allowed to trade but that "it's not something they can do indefinitely."

Not only were the shares trading, but volume on each was extremely heavy. As of 10:30 a.m., just over an hour into the session, over 20 million shares of Delta had changed hands and over 75 million had traded of Northwest. The average daily volume is 12 million and 9.5 million, respectively.

Delta and Northwest filed for Chapter 11 after the close of trading Wednesday after being squeezed by cutthroat competition over the last several years and soaring fuel prices over the last several months.

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