ATLANTA: Airline shares and oil prices used to move together like kids on a teeter-totter, with one rising while the other falls. But the financial crisis affecting the U.S. and other countries has thrown that conventional wisdom out the window.

Investing in airlines for the long-term can be a risky and not always rewarding proposition, as four major U.S. carriers have filed for bankruptcy protection since 2002, wiping out their pre-Chapter 11 shares in the process. Fort Worth, Texas-based AMR Corp., parent of American Airlines, which avoided bankruptcy, has not paid a dividend to common shareholders since 1980, a spokesman said.

For much of the third quarter, some short-term investors were able to make money from big swings in airline shares that had more to do with the price of oil than the fate of Wall Street firms. But the broad reach of the financial crisis may have severed that connection.

''In the past two weeks, it's a different story,'' Calyon Securities airline analyst Ray Neidl said. ''The credit markets are affecting the overall market and that's what is affecting everyone and what the impact will be for airlines in terms of demand.''

As oil prices plunged about 38 percent from around $147 a barrel on July 11 to around $91 a barrel on Sept. 16, shares of the big six legacy carriers soared — in Tempe, Ariz.-based US Airways Group Inc.'s case, its stock more than quadrupled over that period. The Dow Jones industrial average was nearly unchanged.

From that point through last Wednesday, oil prices fell another 2 percent to around $89 a barrel, but shares of the six airlines sank.

In the case of Chicago-based UAL Corp., parent of United Airlines, its stock shed more than half its value over the three-week period. The Dow, meanwhile, fell about 1,800 points, or roughly 16 percent.

''The old saying is, 'You can't fight the tape,' and that's what airline stocks are up against right now,'' Neidl said.

Stifel, Nicolaus & Co. analyst Hunter Keay said in a recent research note that he sees significant upside potential for domestic airlines, particularly shares of Atlanta-based Delta Air Lines Inc., which he believes are significantly undervalued. The carrier expects to close its acquisition of Eagan, Minn.-based Northwest Airlines Corp. later this year.

Several major airlines have moved aggressively to shore up their cash positions. The specter of bankruptcy that was back on airlines' and analysts' radar screens in May has seemed to diminish in the months since. Some airlines, which have benefited from significant capacity cuts and new fees they have been charging customers, have even been talking about posting profits in the future.

''Right now, they seem to have things pretty well controlled with their capacity reductions,'' Minneapolis airline expert Terry Trippler said. ''The last eight flights I have been on, all but one have been filled — and this is with higher prices and fees.''

For now at least, airline investors seem to be largely ignoring carriers' improved balance sheets. With the U.S. economy in deep turmoil, could investors be worried about demand for air travel falling off in the future?

''I think the airlines have a handle on it right now,'' Trippler said. ''Going forward, they will have to watch it very closely.''

Airlines for the most part have been able to weather the problems created by the frozen credit market. That's because they have been able to tap existing credit lines or sell assets to raise cash. But experts have said the longer credit markets stay tight, the longer many companies will have to draw down their reserves and credit lines.

If the airlines are worried, they aren't saying.

Officials at several major carriers declined to comment or did not respond to interview requests. Investors will get a fresh look at U.S. airlines' prospects for the future when carriers release third-quarter results.

What the future holds for long-term airline shareholders, who have been craving a return on their investments, remains to be seen.

Trippler said airline shares are likely to continue to fluctuate.

''Airline stocks have never been a hold,'' he said. ''They've always been a buy or sell kind of stock.''