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 convenience-store operator Casey's General Stores (Nasdaq: CASY) were sputtering today, falling as much as 13% in intraday trading after the company reported fiscal fourth-quarter results.

So what: The short story is this: Wall Street thought that Casey's was going to earn $0.67 for the quarter and the company reported $0.60.

The company pointed to squished margins on gasoline, bringing down the per-barrel margin $0.02 versus last year. While that may not sound like much, consider that the total margin per gallon was just 13.7 cents. Management said the lower gas margin shaved $0.12 off of the company's earnings per share.

Notably, though, it was a rise in operating expenses that had a lot to do with Casey's year-over-year flatlining (it reported $0.60 in EPS last year, too). Gross profit was up almost 13% from the fourth quarter of 2011, but operating expenses increased 17% and the total dollar increase in operating costs almost completely offset the increase in gross profit. Management chalked up this increase to new and remodeled stores.

Now what: There are actually some bright spots that investors can take away from the quarterly report. Same-store sales for groceries and other merchandise were up 8.5% for the quarter, while prepared food notched a 16.8% same-store-sales jump. Both also reported margins that were above the prior year's level. Though gasoline sales are far greater than either of those other segments, they are both larger contributors to Casey's gross profit.

It's rare that a company can report results below Wall Street's expectations and not see its stock get walloped. Casey's stock isn't particularly cheap -- so investors are obviously expecting solid growth -- but I think there's more good to this quarter than the trading action gives credit for.

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