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 all-American refinery operator Western Refining (NYSE: WNR) hit a dry spell today, falling as much as 20.1% on fairly heavy volume.

So what: Western Refining's second-quarter sales and earnings fell short of Wall Street's targets -- on perhaps the worst of all possible days. From minnows such as Delek US Holdings (NYSE: DK) and Western Refining to giants Valero Energy (NYSE: VLO) and Chevron (NYSE: CVX), the petroleum sector is littered with big falls today for a variety of reasons.

Now what: This is just one in a stable full of disappointing oil reports this week, coupled with economic worries and even a potential oil disaster caused by rising waters in the Missouri River. Crude oil prices are also down to their lowest levels since February, easing consumer pressure at the pump but adding to the industry's panic. Let me just remind you that BP (NYSE: BP) posted better-than-50% gains since last year's Gulf of Mexico disaster and even reinstated its generous dividend after a brief halt. I've never owned an oil stock, but if I ever buy in this industry, it'd be while the streets are running with a mixture of blood and oil -- like today.

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