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 US Airways Group's case, its stock more than quadrupled over that period. The Dow Jones industrial average was nearly unchanged. From then through Wednesday, oil prices fell another 2 percent, but shares of the six airlines sank — in the case of Chicago-based UAL, 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.