You've heard of the "January Effect," where investors sell stocks in December for tax reasons, only to buy them back in January, causing their prices to jump.

What about other months? Retailers, for example, perform better in some seasons than others, simply because of the nature of the business. Some stocks even do better in August. Whatever the reason, investing based solely on the calendar is certainly not a Foolish strategy.

Still, wouldn't it be great to know ahead of time which stocks performed best at what times?

On Motley Fool CAPS, more than 115,000 members have weighed in on more than 5,500 stocks, awarding five-star ratings to the companies that command their confidence. We've paired their opinions with data going as far back as five years to see which stocks perform best in each month. The following five companies seem to do best in August:

Stock

Market Cap

Avg. % Return: August

Avg. % Return: Rest of Year

CAPS Rating (out of 5 max)

YTD Return

Energy Conversion Devices (NASDAQ:ENER)

$3.05 billion

16.26%

3.96%

***

108.9%

W.R. Grace (NYSE:GRA)

$1.9 billion

16.91%

4.09%

**

5.8%

Excel Maritime (NYSE:EXM)

$1.8 billion

51.13%

8.63%

****

0.3%

Gulfport Energy (NASDAQ:GPOR)

$585 million

20.56%

2.54%

*****

(27.6%)

Autodesk (NASDAQ:ADSK)

$7.4 billion

13.62%

2.12%

*****

(28.9%)

Sources: America Online, Motley Fool CAPS as of Aug. 14.

What's driven the outsized August performance of Louisiana oil and gas producer Gulfport Energy, even though another such producer, Apache (NYSE:APA), does better in September? This is one reason why we don't recommend using this as simply a list of stocks to buy or sell -- just a platform for further research. We need to look closer for the reason, but Gulfport Energy's five-star CAPS rating suggests it will continue pumping out returns for investors. And let's see which of the other companies above might live up to the promise of this month.

Full of energy
CAPS member kkinva68 takes a look at everything that Energy Conversion Devices is involved with -- it's so much more than just batteries -- and sees the potential for continued, outsized growth.

This is not just a solar company,it is a computer memory company and a battery company. It just sold new shares to professional investors @ $72 so how can it not be a buy at $61.08??? Those new shares are for increased manufacturing capacity so the company can keep up with demand... good all around ... hopefully GM will close on taking the battery plant (cobasys) off [their] hands soon…

UNI-SOLAR thin-film flexible solar laminates will power the world's largest rooftop solar power system. The 12-megawatt system is being installed on GM's assembly plant in Figueruelas, Zaragoza, Spain and will become operational in the fall of 2008. ECD will supply the solar laminates through its wholly owned subsidiary, United Solar Ovonic, LLC.

Indicates that the companies are still on good terms.

Competitor [First Solar Nasdaq: FSLR]=$264/share

Ship ahoy!
Similarly, CAPS member ricardols2000 looks at the economics behind bulk shipper Excel Maritime and sees enough upside to justify the costs involved in shipbuilding.

EXm and most bulk shippers are full of cash. It costs [about] Uss 8000.00 a day to run a ship,and the market is paying 85000.00 Uss per day for a Panamax on a one [year] charter,if its less than 8 [years] in age.I recently saw a fixture for a ship being constructed and to be delivered in late 2009 at a figure similar to above. The index is now at 9200 after being at 11500 or so… This stock has too many Panamax on long charter till 2010 with Bunge at Uss 24000,00 a day (originally [fixed] with Quintana),so lets hope the market holds steady so they can get some capital appreciation on the vessels.

A calming effect
It pays to start your own research on these stocks on Motley Fool CAPS. Read a company's financial reports, scrutinize key data and charts, and examine the comments your fellow investors have made -- all from a stock's CAPS page. Because it's free to sign up and express your investing opinions, why not use this opportunity to take your star turn?

Try any of our Foolish newsletters today, free for 30 days.

Fool contributor Rich Duprey does not have a financial position in any of the stocks mentioned in this article. You can see his holdings. The Motley Fool has a disclosure policy.