A thought-provoking article in BusinessWeek magazine the other day listed companies with the biggest pension-funding deficits. In descending order, the culprits were ExxonMobil (NYSE:XOM), Ford (NYSE:F), Delta Airlines, Lockheed Martin, and General Motors (NYSE:GM). I can understand how most of those firms made the list -- but not ExxonMobil.

Ford, General Motors, and Delta have been fighting for their health, if not their lives, in recent years. Heck, Delta even filed for bankruptcy last year. I'm less familiar with Lockheed Martin, but fellow Fool Jeremy MacNealy's recent report suggests the company has enjoyed strong financial results during wartime. In addition to the companies on that chart, many other major corporations have underfunded pension plans, including Boeing (NYSE:BA), Pfizer (NYSE:PFE), Procter & Gamble (NYSE:PG), and ConocoPhillips (NYSE:COP).

But ExxonMobil, despite its massive unfunded pension plan obligations, is clearly not struggling. It's been posting record financial results lately, with some $8.4 billion in net income in its last quarter alone. Its net income in 2005 was $36 billion, up from $25 billion in 2004. Revenues in 2005: $371 billion! And to top it off, the company's departing CEO Lee Raymond received a severance package worth $400 million.

All that certainly doesn't suggest a company struggling to make ends meet, yet the difference between ExxonMobil's pension-plan assets and its projected benefit obligations (per generally accepted accounting principles, or GAAP) tops $11 billion. All my reading on the perilous state of many pensions in our country has me wired to see pension underfunding as irresponsible and reckless -- especially an instance involving an $11.2 billion shortfall. Maybe you feel the same way.

Still, here's something to keep in mind: Take a gander at ExxonMobil's balance sheet, and you'll find more than $36 billion in cash. In other words, if the company needed to wipe out its pension plan deficit in short order, it could take that $11.2 billion out of its local bank's ATM immediately. The company seems to be firing on all cylinders right now. Its return on invested capital was a substantial 31% in 2005, up from 24% in 2004, 21% in 2003, and 13.5% in 2002.

So there's no problem, right? Well, not right now. But those pension payments will come due over the next years or decades. Will the company still have $36 billion in the bank by then? As the BusinessWeek article points out, paraphrasing pension consultant and actuary John W. Ehrhardt, "If bankrupt airlines, steelmakers, and auto parts suppliers had contributed extra cash to their pension accounts during their good years, today's pension crisis probably wouldn't be nearly so severe."

Amen.

ExxonMobil employees (and shareholders, for that matter) should remember that though the firm seems very healthy right now, especially compared with some other pension-challenged firms, no retirement benefits should be taken for granted. It's always smart to save and invest on your own, in order to build the most secure retirement you can. If you'd like some help, my own favorite retirement information resource is the Fool's Rule Your Retirement newsletter, edited by Robert Brokamp, which you can try for free.

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Longtime Fool contributor Selena Maranjian owns shares of Pfizer, a Motley Fool Inside Value pick. The Fool has a disclosure policy.