Just months ago, the credit market was exceptionally tight. In spite of (or perhaps because of) Uncle Sam's help, almost no company that actually needed a loan was able to get one from a private lender at decent rates.

In fact, those that could get money at all were forced to pay outrageous interest for the privilege. General Electric, for instance, is paying Berkshire Hathaway 10% on its preferred shares, and GE had to sweeten the pot with warrants to get its rate that low.

And GE is a profitable industrial titan -- once the world's largest company -- which, even after its downgrade, still sports an impressive AA+ debt rating. When a company like that needed to dilute its shares to get a loan at double-digit rates, you know the credit market was tight. Although it was difficult and expensive, GE could borrow the cash it needed to operate. These days, not everyone is so lucky.

Who's the most at risk?
The credit market remains tricky. And in a tricky credit environment, companies that can't either roll over their debt, or pay their debt and operate with what they have, are in danger of going under.

But with the possible exception of law firms that handle bankruptcies, nearly every company is feeling the pain of this economic downturn. So how can you tell whether a company is struggling just like everyone else -- or about to fail?

These three signs should make you sit up and take notice:

  • Substantial debt. Given this credit market, a company with significant debt that it can't pay off is a huge risk for shareholders.
  • Negative tangible book value. This means that a company's total worth is tied up in its brands, its goodwill, and its ability to generate cash, leaving nothing physical to borrow against.
  • Negative earnings. These signal that the company hasn't been able to run its business profitably in recent quarters.

When you put all three of those high-risk signs together, you get companies like these:

Company

Tangible Book Value
(in millions)

TTM Net Income
(in millions)

Total Debt
(in millions)

Marriott (NYSE: MAR)

($548)

($240)

$3,269

Crown Castle International (NYSE: CCI)

($1,684)

($244)

$6,741

UAL Corporation (Nasdaq: UAUA)

($5,326)

($351)

$9,304

Dex One (NYSE: DEXO)

($9,077)

($6,453)

$3,084

ArvinMeritor (NYSE: ARM)

($1,600)

($251)

$1,090

Leap Wireless International (Nasdaq: LEAP)

($686)

($240)

$2,756

Fannie Mae (NYSE: FNM)

($96,620)

($71,969)

$774,554

Data from Capital IQ, a division of Standard & Poor's.
TTM = Trailing 12 months.

Of course, not every company that shares these traits is on the verge of failure, and I'm not suggesting that the above companies are literally about to fail. Marriott, Dex One, and UAL, for instance, owe much of their losses to asset write downs. While that's often a sign of overly optimistic expansion plans gone astray, it's hardly a corporate death sentence.

Similarly, Crown Castle is in the capital intensive telecommunications infrastructure business, and much of its financial pain seems to reflect financing hurts. And although ArvinMeritor is closely tied to the troubled auto industry, its recent strength makes it look more like a survivor, rather than part of the next wave of carnage.

On the other hand, those three signs in combination often tell of darker days to come. Indeed, Fannie Mae was at the center of the financial meltdown that nearly destroyed the economy, and it survives only thanks to continued government support. Likewise, UAL, the parent company of United Airlines, is no stranger to the bankruptcy court, and Dex One is the post-bankruptcy reincarnation of the former R H Donnelly.

And while it's not exactly a death sentence, Leap Wireless has put itself up for sale, which, in its current financial condition, isn't exactly a sign of strength, either.

If a company is in debt, doesn't have enough assets to borrow against, and isn't earning profits, then it's only a matter of time before its debt holders get tired of financing its business. That's especially true now.

Buy smarter
In general, companies that hemorrhage cash, have weak balance sheets, and are drowning in debt make lousy investments. On the flip side, stocks that gush cash, make smart use of debt, and have solid balance sheets backing up their businesses can be tremendous companies to own.

That's especially true during times like these, when virtually every company has been knocked off its peak, and even some of the strongest ones are available at bargain-basement prices.

At Motley Fool Inside Value, we're actively scouring the market to find the solid companies whose shares have been left to rot alongside the truly damaged ones. When we find those diamonds in the rough, we share them with our members, who then have the opportunity to buy some of the world's greatest companies at bargain prices.

If you're ready to avoid the companies teetering on the edge of failure, and instead focus on those with the fundamental strength to thrive in the long run, join us at Inside Value. Simply click here to learn more or start your 30-day free trial.

This article was originally published March 10, 2009. It has been updated. 

Editor's note: A previous version of this article contained an incorrect figure for Dex One's debt. The Fool regrets the error.

At the time of publication, Fool contributor and Inside Value team member Chuck Saletta owned shares of General Electric. The Motley Fool owns shares of Berkshire Hathaway, which is both a Motley Fool Stock Advisor selection and an Inside Value pick. The Fool has a disclosure policy.