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 Whiting Petroleum (NYSE: WLL) fell 12% in intraday trading today as the market sold off oil and gas explorers and producers.

So what: Oil is down more than 2% today, and the market is concerned about a Greek default affecting economic growth going forward. Add all of this together and we have a massive selling of any company related to the oil and gas sector.

Now what: The sell-off has gained momentum throughout the day, and the SPDR S&P Oil & Gas Exploration & Production ETF (AMEX: XOP) has fallen 6% as of this writing. That's a massive drop for an ETF with a large number of stocks in it, but it shows how widespread the selling is. These stocks will eventually rebound, but calling a bottom is a risky proposition with the market in full on freak-out mode right now.

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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.