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: Oil exploration and production company TransGlobe Energy (Nasdaq: TGA) dropped more than 8% today in heavier than average trading volume. The Canadian company has oil interests in Egypt and Yemen.

So what: TransGlobe released a mid-quarter business update after market close on Monday that reiterated its production estimates of 13,000 to 13,500 barrels per day for 2011 and its estimated capital expenditures. It also reported output for the first 12 days of December of 11,600 barrels per day, higher than its 11,000 target, and up 6% from November.

But that news was overshadowed by bad news about the company's Egyptian interests. TransGlobe reduced its estimates of the oil pool acreage at a location in West Gharib, Egypt, and drilled a well containing water, a disappointing result after drilling a 2,000-barrel-per-day well nearby.

Now what: Prior to today's drop, TransGlobe's stock was up nearly 400% for the year. Given the appreciation in shares, a sell-off driven by a mixed report from the company shouldn't be too surprising, and it gives investors who remain bullish on the company's longer-term prospects a more attractive buying price.

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Fool contributor April Taylor does not own shares of the companies mentioned. Try any of our Foolish newsletter services free for 30 days. 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.