Just one in five U.S. pension plans has enough assets to meet obligations, a state of affairs caused largely by overly optimistic projections of investment returns that points to a range of possible scenarios, from changing benefits to pensions going broke, according to a study from Cogent Research.

About 54 percent of public pensions say their current funding status is below 80 percent of what is necessary to meet their obligations, and 16 percent of the pensions are below 60 percent of what they’ll need, according to Cogent’s “Institutional Investor Brandscape” study.

This shortfall is even more acute among the largest pensions, and especially among union and public sector plans, where only 10 percent and 12 percent of them, respectively, estimate their current funding status is 95 percent or higher.

“These are very sobering numbers,” Christy White, the report’s author and a principal at Cogent, said in a press release.

“Half of all public pensions are substantially underfunded, which means these institutions face several extremely difficult choices,” White added, saying choices range from taxpayer-funded bailouts, to different payments to even going broke.

However, corporate pensions appear to be in much better shape, a reflection that they have made some of the tough choices to avoid becoming underfunded, “no doubt at the behest of shareholders and investors,” White said.

Among corporate pensions, more than a quarter are funded at 95 percent of what they’ll need; more than half are funded between 80 percent and 94 percent and none reported a funding status below 60 percent.

Despite the relatively rosy picture in the corporate sector, Cogent principal John Meunier believes the underfunding may be worse than the study depicted.

“Underlying current funding status estimates are performance projections that for many institutions may be overly optimistic,” Meunier said in the press release.

“Course corrections will be painful to say the least, and the kind of leadership and shared sacrifice required to make the necessary changes to pensions are in short supply,” he added.

The report is based on a survey among a nationally representative sample of 590 institutions with a minimum of $20 million in assets.

Cogent released results of another part of the study earlier this month that found that Pimco, the world’s largest bond fund manager, and Boston-based asset manager Loomis Sayles were the most popular asset managers among institutional investors.

Cambridge, Mass.-based Cogent was founded in 1996.