Corporate pensions are in worse shape than they've ever been, according to a couple of measures tracked by consulting firm Mercer.  At the end of August, the pension funds at 1,500 large publicly traded companies were $506 billion in the red, which means they had money to pay just 71 percent of their obligations.

At the end of December, the same plans were 84 percent funded. The weak stock market accounts for some of the decline, but falling interest rates are the big culprit. When actuaries calculate the present value of a future liability, that value depends on the interest rate they use. A lower interest rate means a bigger liability.The average corporate AA bond yield, at 4.94 percent, is the lowest in a decade, Mercer says.

The widening gap will show up on corporate balance sheets at year's end, says Mercer expert Gordon Young:

If the low funded status persists until the end of 2010 ... net balance sheet liabilities and income statement expense for 2011 will increase significantly for many companies. Cash contributions will also need to increase to reduce the deficit. Some of this may be mitigated by various smoothing methods and pension funding relief, but nonetheless these market conditions will certainly grab the attention of plan sponsors."