Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of American Airlines parent AMR (NYSE: AMR) have plunged today, off by as much as 10%, as the company reported third-quarter earnings results.

So what: Operating revenue rose 9.1% to $6.4 billion, but high fuel costs weighed on the bottom line and the company saw a loss of $162 million, or $0.48 per share. Analysts were looking for revenue of $6.4 billion and a loss of $0.41 per share. AMR said fuel expenses jumped 40% from the prior year.

Now what: American Airlines was the only major airline to show a full-year loss last year and is on track to deliver another full-year loss this year. The company expects volatile fuel prices to continue to cause problems throughout the year. Consolidated passenger revenue per available seat mile increased 8.7% and, the company expects cost per available seat mile excluding fuel and labor costs will jump between 6.2% and 6.6%. Personally, I'll never buy an airline stock for exactly this reason: They are far too dependent on oil prices, which are far too volatile.

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