NEW YORK (CNN/Money) - The market got a bit of a surprise late Wednesday when Honeywell said in a filing that it expects it will have to pump between $235 million and $335 million into its pension plan next year. But the real shock was that investors apparently didn't see it coming.

Even as the market jumped higher Thursday, Honeywell shares fell 8.3 percent, leaving the Wall Streeters and accounting experts who have been closely following the pension issue scratching their heads. That Honeywell's, like many other companies', pension fund was coming up short should hardly have been a surprise.

Pain to come These companies' pension plans look like they'll be the most underfunded at year end. Company  Estimated underfunding  General Motors  $29.4 billion  Ford  $14.3  IBM  $13.3  Exxon Mobil  $9.4  Boeing  $6.8  United Technologies  $4.7  Lockheed Martin  $4.4  Delta  $4.4  Delphi  $4.2  Raytheon  $3.6   Source:  Credit Suisse First Boston

"Who said the market was efficient?" said Harvard Business School professor David Hawkins, who advises Merrill Lynch on accounting issues. "Every major firm on Wall Street has put out a study on this. I guess investors just didn't think it was real."

If that's the case, then investors are in for many more unpleasant surprises. Honeywell's announcement is just the beginning.

"The pension problem is not specific to Honeywell," said Credit Suisse Asset Management managing director Stanley Nabi. "A lot of companies are going to come out between now and the end of the year and say that they're underfunded."

For many years, nobody had to worry about pensions. The stock market was bubbling along and company pension plans were bubbling along with it. That meant companies could cut the checks going out to retired employees without having to contribute any further money to the pension plan.

But now with a third down year in a row in the market, pension plans are running into trouble. Many have fallen to the point where companies are going to have to start coughing up dough to keep on paying off their current and future retirees, like Honeywell expects to do.

Credit Suisse First Boston's accounting specialists estimate that as many as 325 of the companies in the S&P 500 could be underfunded at the end of this year, to the tune of $235 billion. Honeywell (HON: Research, Estimates), whose pension fund Credit Suisse expects will close out the year $2.5 billion underfunded, is one of them.

But hardly the worst: General Motors' plan looks like it will be $29.4 billion underfunded at the end of the year, according to Credit Suisse. The company hasn't said what it's going to do about that yet, but in its latest quarterly filing it said that, assuming pension-plan returns of 8 percent to 10 percent per year from 2003 to 2006, it will have to pump $14 billion to $17 billion into its pension plan.

Since General Motors (GM: Research, Estimates) is something of a poster child for troubled plans, maybe its shareholders are already prepared for pension pain. Ditto Ford (F: Research, Estimates) and IBM (IBM: Research, Estimates). But there are a mess of companies, like Honeywell, whose pension problems haven't been written up in the papers but who have problems nonetheless. Pension bombshells could be a regular occurrence in the months to come.

"People are just putting this under the carpet," said Larry Rice, vice president at Janney Montgomery Scott. "There are plenty more companies out there that are going to have this problem."