At The Motley Fool, we poke plenty of fun at Wall Street analysts and their endless cycle of upgrades, downgrades, and "initiating coverage at neutral." So you might think we'd be the last people to give virtual ink to such "news." And we would be -- if that were all we were doing.

But in "This Just In," we don't simply tell you what the analysts said. We'll also show you whether they know what they're talking about. To help, we've enlisted Motley Fool CAPS, our tool for rating stocks and analysts alike. With CAPS, we'll be tracking the long-term performance of Wall Street's best and brightest -- and its worst and sorriest, too.

And speaking of the worst ...
Trivia question: When I say "Oppenheimer," what's the energy source that first comes to mind?

OK, that wasn't so hard. The answer is "nuclear energy." For better or for worse, Manhattan Project head Dr. Robert Oppenheimer's name will always be linked with the phrase "father of the atomic bomb." But what about investment banker Oppenheimer? Its reputation may well be determined by the upgrade it issued this morning, a blanket endorsement of just about every company on the planet that has anything to do with oil.

BP (NYSE:BP), Chevron (NYSE:CVX), ConocoPhillips (NYSE:COP), ExxonMobil (NYSE:XOM), Frontier Oil (NYSE:FTO), Valero Energy (NYSE:VLO), XTO Energy (NYSE:XTO), and more than a dozen others received seemingly indiscriminate buy endorsements from Oppenheimer, which played Father Christmas to the hydrocarbon set this week.
 
In a research report titled "Now Is The Time to Buy Oil and Gas Stocks," Oppenheimer makes the case for buying the whole industry en masse. The analyst doesn't tell us to "buy some oil and gas stocks" or "buy the best oil and gas stocks" -- just buy 'em all. Of the 20 new ratings that appeared in Oppenheimer's report, each and every one was certified buy-rated. Not a hold in the bunch, and not a single sell either.

This, at a time when fellow big banker Deutsche Bank is now predicting that oil will fall as low as $50 a barrel. Amazing.

But true
Investors are buying both Oppenheimer's argument, and its favorite stocks. So far today, Conoco is already up 4%, Chevron 7%, and BP 11%.

Now, I don't mean to be a wet blanket. In a market like this one, I'm as starved for good news as anyone. I haven't seen a green ticker in so long, I may need to visit the eye doc and check for color-blindness. So I'd love -- love -- to see Oppenheimer proved right. But ...

Facts are stubborn things
Problem is, statistics tell us that Oppenheimer is probably wrong on more than half of these bullish energy calls. We've been tracking this banker's performance in CAPS for more than two years now, you know. And according to our CAPS data, Oppenheimer guesses wrong on its stock picks roughly 58% of the time.

How bad is that? Bad enough that the banker performs worse than 80% of the investors we track. Bad enough that, on average, any company Oppenheimer picks underperforms the S&P 500 by more than three percentage points.

Foolish takeaway
Don't get me wrong. Not all of Oppenheimer's picks today will be proven wrong over time. In fact, a quick scan of the numbers suggests that the analyst is most likely right in endorsing Conoco, Frontier Oil, and XTO -- all of which sell for very attractive PEG ratios.

Moral of the story: Sure, there are bargains out there, in oil and elsewhere. Heck, in a market as manic-turned-depressive as this one, there can't help but be bargains on offer, babies tossed out with bathwater, and gorgeous values for the asking. But blindly following blanket buy ratings from a not-very-good analyst is not the way to find them. Do your own due diligence before following Oppenheimer's advice.

Fool contributor Rich Smith does not own shares of any company named above. You can find him on CAPS, publicly pontificating under the handle TMFDitty, where he's currently ranked No. 521 out of more than 120,000 members. The Fool has a disclosure policy.