Delta Air Lines (DAL) shares shot higher Thursday, one day after it declared bankruptcy as expected, but Northwest Airlines (NWAC) stock plunged as it surprised investors by also seeking Chapter 11.

Shares in Northwest dropped more than 50 percent as investors dumped them after the company surprised the Street and filed for Chapter 11 federal bankruptcy protection, while Delta shares rose more than 30 percent.

Delta and Northwest, the third- and fourth-largest U.S. air carriers, both declared bankruptcy on Wednesday as the industry's struggle with soaring oil prices and low-cost competition led to one of its darkest days.

While Wall Street took different takes on each filing, one analyst said this kind of stock disparity is not that unique.

"I've seen it with other bankruptcies," said Susan Donofrio, an analyst at Fulcrum Global Partners. "I think it really has to do with retail investors and airline customers. They hear about a filing, they see an aircraft flying and they assume there's some value on the stock and that they're going to get it at a bargain."

While Delta's filing had been long expected, Northwest's came as a surprise to many on Wall Street, including analysts at blue-chip securities firms J.P. Morgan and Morgan Stanley, who reiterated their "overweight" ratings on its stock before the filings.

The New York Stock Exchange (search) on Thursday said it is reviewing the listing status of Delta's common stock and related securities. The Exchange has suspended trading in Northwest's debt securities, and said it would move to delist those securities.

Wall Street analysts also weighed in on the airlines.

Until Thursday, Prudential analyst Bob McAdoo had an "overweight" rating on Northwest shares. However, he cut the rating to "underweight" following the Chapter 11 filing. Fulcrum Global Partners had a "buy" rating on Northwest until Thursday, when it downgraded it to "sell."

The analysts stuck by the Eagan, Minnesota-based airline even after Northwest's pilots disclosed the airline's board was set to consider whether to seek a bankruptcy filing.

Northwest shares were down 49 percent at 95 cents each, after plunging more than 52 percent earlier in the morning. Delta shares, however, rose 31 percent to 93 cents on the New York Stock Exchange.

Northwest's stock has plunged 86 percent so far this year, while Delta has lost more than 90 percent of its value.

Both carriers' stocks will also be deleted from the Dow Jones Transportation Average (search) at the close of business on Friday, Dow Jones said.

Bankrupt companies' shares often continue to trade, as they have with airlines UAL Corp. (search) and US Airways Group Inc. (search) , but their value is typically wiped out.

Delta is set to embark on Thursday on what may be a long march through Chapter 11 with its first public hearing in U.S. Bankruptcy Court in Manhattan. The hearing will clear the way for Delta to start rejecting aircraft leases as it begins to shrink its fleet as part of the reorganization process.

Both Delta and Northwest made clear on Wednesday that they will focus on eliminating what they see as an excess of available seats by reducing flights and switching to smaller planes on some routes.

Those moves will almost certainly lead to further layoffs at both, though neither airline said how many. That would add to headaches for once well-paid airline workers.

Their pensions are also up in the air as both have made clear they are unable to honor their current retiree commitments.

Northwest's Chief Executive Doug Steenland (search) said on Wednesday that the airline hoped to avoid a wholesale dumping of pensions like the one earlier this year at United Airlines that infuriated workers and politicians.

Both airlines may cancel orders for planes from Boeing Co. and European archrival Airbus, making the bankruptcies a potential negative for their shares, though analysts said the planemakers would have little trouble placing their aircraft elsewhere.

Delta's filing could, however, hurt its leasing companies. Computer services company Electronic Data Systems Corp. on Thursday said it will take a third-quarter charge to write down the value of its aircraft leases with Delta Airlines. Walt Disney Co. (DIS) on Wednesday said it may have to write down $100 million of Delta leases.