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: Forest Oil (NYSE: FST) dropped 15% in intraday trading today after it announced disappointing preliminary second-quarter results and 2011 guidance.

So what: The update didn't provide EPS guidance but discussed second-quarter volumes and anticipated second-half volumes and expenses. It was enough information for analysts to dramatically cut their EPS estimates.

Now what: The second quarter marks the seventh earnings disappointment in the last eight quarters. One analyst said flooding in Louisiana, plant downtime in Texas, and the sale of some Texas property were affecting results. The company is in the midst of spinning off its Canadian assets and increasing its oil development efforts, further complicating forecasting.

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Fool contributor Cindy Johnson does not own shares of any company named above. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.