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NEW YORK (CNN/Money) - Analysts were downgrading Federal Express last fall. But since December, four firms have upped their ratings. This change in sentiment has yet to be reflected in the stock price, however. At a current $90 a share, Federal Express is nearly 12 percent below its 2005 high.

This discount is puzzling. Long-term consensus earnings projections for FedEx call for impressive 15 percent compound annual growth. Nonetheless, the shares are trading at less than 19 times earnings for the fiscal year ending May 31, and less than 17 times estimated results for the fiscal year that's just beginning.

Business is nothing to complain about either. Earnings rose 51 percent rise on a 21 percent revenue increase in the third fiscal quarter. And analysts expect that earnings for the fourth quarter will show a double-digit profit gain.

If everything looks so good, why isn't the stock trading higher? There are three reasons -- and in my view, each seems like an argument to buy.

For starters, Federal Express is a highly seasonal stock. Business tends to be slack in the summer, but picks up once people start shipping lots of things in the fall.

As a result, over the past five years, FedEx stock has risen an average of 16 percent between June 1 and year-end. In two of those years, the gains were only single-digit. But gains in the other three years were sizable.

The second factor weighing on the share price is the cost of gasoline and jet fuel, which in turn depends on the price of oil. So far, FedEx has been successful in absorbing these costs or passing them through to customers. In fact, profit margins for the carrier services actually rose in the third fiscal quarter.

Analysts worry that a continuation of high oil prices will eventually begin to erode margins. That may be true. But that also means that a decline in the oil price would be extremely bullish for the stock. And I continue to think that the oil price will eventually ease.

The final argument for the stock is that FedEx has yet to realize significant benefits from its 2004 acquisition of Kinko's. That division's margins were skimpy in the most recent quarter, but FedEx still expects that the acquisition will pay off once the process of absorbing and integrating Kinko's is completed.

In short, FedEx (Research) could benefit from a seasonal upswing, from an easing of the oil price or from the workout of last year's big acquisition. And with the earnings potential of a growth stock, the shares are trading at only a market P/E.

Sivy on Stocks resources:

Sivy 70: America's best stocks

Guide to Growth

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Michael Sivy is an editor-at-large for MONEY magazine. Click here to receive Sivy on Stocks via e-mail every Tuesday.