"'Don't catch a falling knife' ... The idea of buying a former superstar stock at a discount price certainly has its attractions, but you've got to make sure you catch the haft -- not the blade."

That's the thesis of my recurring Fool column "Get Ready for the Bounce," in which we search the wreckage of Mr. Market's overturned cutlery drawer for future winners. But do we really need to sit around for a whole year, waiting for a potential bouncer?

Nope. Sometimes, stocks fall far in far less time than a year -- and like a superball dropped from the balcony, the harder they fall, the higher they bounce. Today, we're going to look at a few equities that've suffered dramatic drops over the past week. With a little help from the 150,000 members of Motley Fool CAPS, we hope to find an opportunity or two for you:

Companies

How far from 52-week high?

Recent Price

CAPS Rating (out of 5)

Petrobras (NYSE: PBR)

-19%

$43.11

*****

UnitedHealth Group (NYSE: UNH)

-10%

$32.63

****

United States Natural Gas (NYSE: UNG)

-60%

$7.00

****

Coeur d`Alene Mines (NYSE: CDE)

-41%

$14.55

****

Barrick Gold (NYSE: ABX)

-22%

$37.41

***

Companies are selected by screening on finviz.com for abrupt 5% or greater price drops over the past week. 52-week high and recent price data provided by finviz.com. CAPS ratings from Motley Fool CAPS.

Five super falls -- one superball
Last week was rough for investors in these five companies -- but the reasons for their troubles weren't always clear.

Take Barrick, for instance. The company completed a successful spinoff of its African Barrick Gold subsidiary last week. But should the loss of those assets really have decreased the value of Barrick's stock, when the company netted $834 million in proceeds from the sale? Or did Barrick simply suffer from the same problem afflicting Coeur d' Alene -- the debt downgrade in Portugal, which bolstered the U.S. dollar, putting corresponding pressure on the dollar-price of gold? (For the record, that's not a rhetorical question. Click over to Motley Fool CAPS and tell us what you think.)

In contrast, the reasons for price drops at UnitedHealth, US Natural Gas, and Petrobras are much easier to discern. The first was certainly a response to passage of Obamacare last week. The second -- a reaction to the rapidly evaporating value of natural gas. And the third ... why, that's this week's story.

The bull case for Petrobras
The big worry about Petrobras last week came down to just two words: cash and debt. With $220 billion in capital spending planned for the next five years, Petrobras lacks enough of the former, and may need to take on more of the latter (perhaps with a loan from China). There's also word that the company may need to dilute existing shareholders by issuing new preferred shares in an effort to raise more cash to fund its projects. Regardless, CAPS All-Star tatihz likes Petrobras as a play on Brazil, since it's "the biggest player in the Brazilian stock market and ... still finding (lots of) oil and expanding."

Bsaun calls the company: "Financially Sound and Stable," offering "Good Growth, Strong Operations & Management."

Meanwhile, kahunacfa believes Petrobras has "truely Monster potential over the next five years and decade." And perhaps beyond: "The company is asset rich and has an active exploration program to find more."

No arguing with that. According to its most recent report, Petrobras boasted 10.3 billion barrels of proven oil reserves, putting it among the world's top publicly traded oil giants, within spitting distance of BP (NYSE: BP) and ExxonMobil (NYSE: XOM). Valued at current spot prices, Petrobras's proven reserves are worth $827 billion. Toss Petrobras's 11 trillion cubic feet of gas reserves into the mix, value them as "barrels of oil equivalent," and the company's energy assets rise in worth to a cool $974 billion.

Yet investors are currently pricing the company that owns these assets at just 22% the value of the assets themselves -- equipment, employees, know-how, all coming gratis. With $179 billion in market cap, and $30.9 billion in net debt, Petrobras carries an enterprise value of $219 billion, or barely one fifth the value of its assets alone.

A steal of a deal?
That sure looks like a bargain. But before you jump on it, consider that two companies that edge Petrobras out in "oil" reserves are selling for even steeper discounts. With even greater portions of their energy reserves being in the form of natural gas -- natural gas that is selling for a song, I might add -- ExxonMobil holds assets worth six times its enterprise value; BP is even cheaper, with assets at seven times the company's enterprise value.

Foolish takeaway
So ... is Petrobras an underpriced stock, due to bounce eventually? Indubitably. Given enough time, I have no doubt that natural gas will eventually regain a price that more accurately reflects its value as an energy source, relative to oil. That said ... there are even bigger bargains available to Foolish investors these days. While Petrobras looks good, Exxon and BP look even better.

But hey, feel free to disagree. If you think Petrobras has more bull potential than BP or Exxon -- I'm willing to listen. Click over to Motley Fool CAPS today, and tell me why.

Petrobras is a Motley Fool Income Investor pick. UnitedHealth is a choice of Inside Value and Stock Advisor. The Fool has opened a diagonal call spread position and written puts on United States Natural Gas. The Fool owns shares of UnitedHealth. Try any of our Foolish newsletter services free for 30 days.

Fool contributor Rich Smith does not own shares of any company named above. You can find Rich on CAPS, publicly pontificating under the handle TMFDitty, where he's currently ranked No. 680 out of more than 160,000 members. The Fool has a disclosure policy.