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: Petroleum Development (Nasdaq: PETD) dropped 13% in intraday trading today after it announced senior management changes on Saturday, and discussed the changes in a conference call this morning.

So what: Chairman and CEO Richard McCullough has resigned. James Trimble, an independent director since 2009, has been named President and CEO effective immediately.

Now what: The unusual timing of the announcement (Saturday) and McCullough's sudden departure suggest that there's some problem management hoped would escape investors' notice. The press release noted that Trimble has guided two privately held oil and gas companies through successful workout solutions, acknowledging that the company may need significant changes. Petroleum Development has struggled to turn a profit even in a favorable pricing environment. It doesn't help that oil prices are declining on concerns about weakening demand.

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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.