Companies representing about 90 percent of all U.S. market capitalization fell another $73 billion deeper into pension funding deficit, according to the latest data from consulting firm Mercer.

Because of a 5.4-percent decline in equities and a fall in yields on high-quality corporate bonds, the aggregated funding deficit for the S&P 1500 increased from $305 billion at the end of July to $378 billion at the end of August, Mercer said. It brings the funded status ratio of the S&P 1500 down to 79 percent compared with 83 percent at the end of July and 81 percent at the end of 2010. The firm's analysis suggests funded status in 2011 peaked at 88 percent at the end of April.

Jonathan Barry, a partner with Mercer's Retirement Risk and Finance Group, says the aggregate funded status for the S&P 1500 bounced around a great deal during the month of August. For pension plans with the common investment allocation of 60 percent in equities and 40 percent in fixed income, monthly volatility in the funded status likely will continue at about 3 percent to 4 percent, he said.

“There certainly is a lot of volatility inherent in pension plans because of the way a lot of plans are invested these days,” Barry says. “We still see a pretty significant mismatch in how assets are invested and how liabilities move, and the market we're in just exacerbates that volatility.”

Mercer says a growing number of pension plan sponsors are taking measures to minimize the effects of such volatility. In addition to freezing plans, sponsors are starting to show increasing interest in changing asset allocations to try to assure changes in plan assets are more closely aligned with changes in plan liabilities. Sponsors also are considering such approaches as encouraging more retirees to take lump sum payments and annuitizing plans, Barry says.