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 airlines were taking a nosedive today as oil prices continued climbing. US Airways (NYSE: LCC) and United Continental (NYSE: UAL) were down as much as 11%, AMR Corp. (NYSE: AMR) fell as much as 8%, while Southwest (NYSE: LUV) experienced a more mild 3% drop.

So what: It's getting increasingly ugly in Libya, and while that means a lot of things -- particularly on the political and human rights fronts -- for the economy it means higher oil prices. And higher oil prices mean higher jet fuel prices, which is bad news for airlines. The group was just starting to recover from the last oil spike and global recession, and crude flirting with $100 per barrel again is not a welcome sight.

Now what: There's a good reason why markets hate uncertainty, and in this case it's because it's unclear what the outcome of the tensions will be in Libya and how long the unrest will last. That also means that it's hard to say what will happen with oil prices. Many of the airlines have stronger balance sheets than they did the last time oil spiked, but that's not really saying much. I don't count myself as a fan of investing in airlines to begin with, but if the pressure from oil prices continues, there may be reason to keep an eye on stronger operators like Southwest.

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Fool contributor Matt Koppenheffer does not own shares of any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy prefers dividends over a sharp stick in the eye.