There may be no more startling inequality gap than that between the CEO office and the average worker.

The 100 largest CEO retirement funds are valued at a combined $4.9 billion, or the entire retirement account savings of 41 percent of American families, according to a new study from the Center for Effective Government and the Institute for Policy Studies.

That means that 100 CEOs have more retirement assets socked away than a combined 50 million U.S. families, or more than 116 million people.

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Billed by the groups as a "tale of two retirements," the study notes that it's more than the mere size of the CEOs' retirement funds that sets them apart. Chief executives are also awarded special savings plans and tax-deferred accounts that allow them to bypass the limits that apply to most Americans. Such loopholes let CEOs set aside huge sums of money without having to pay taxes, depriving the U.S. Treasury and state coffers of tax revenue, the authors noted.

At the same time, some companies are cutting back on their retirement offerings for the rank-and-file as a way to both cut costs and push risk onto their employees. For instance, several Fortune 500 companies have offered lump-sum pension buyouts to employees in the past few years, trading a one-time payment to workers rather than a guaranteed monthly pension payment. Other companies closed pensions to new hires, or froze benefits.

The findings come at a time when many Americans face a major shortfall in funds for retirement, ranging from their own meager savings -- with the median average 401k balance standing at $18,433 -- to next year's flat Social Security payments.

Much of the crisis is framed as a personal failure, with experts directly or implicitly blaming workers for failing to set aside enough for their golden years. That's something Scott Klinger, director of revenue and spending policies at the Center for Effective Government, an advocacy group and think tank, takes issue with.

The retirement crisis is often portrayed "as people aren't saving enough," he said. "There are a lot of incentives that put self-interest ahead of the public interest. There are rules that benefit those with a lot, at the expense of those that don't."

In 2014, 18 percent of private sector workers had a defined benefit pension, the kind of old-school retirement plan that was common decades ago. But because they create more liability for employers, which must bear the costs of providing monthly pension payments to former workers, they've long been fading out in favor of 401(k) plans, which shifts the risk to workers themselves.

That hasn't been the case for CEOs. The groups found that 52 percent of Fortune 500 chief executives were covered by a company-sponsored pension. Some of these pensions are special retirement plans for CEOs and top executives, called supplemental executive retirement plans, or SERPs. More than half of the total retirement assets of CEOs tracked in the report are held in SERPs.

Corporate chiefs also benefit from tax-deferred compensation plans that don't have limits for contributions. By comparison, average workers who are under 50 years old face an $18,000 annual contribution limit for their 401(k)s. These special accounts held $3.2 billion for the 341 Fortune 500 CEOs at the end of 2014, the study found.

Given that CEOs earn far more than the typical American worker, aren't their larger retirement assets simply a result of their outsize pay? That's only part of the story, Klinger said.

"Most companies have made their retirement benefits less generous over the last 10 to 20 years, and CEO retirement benefits have gone up in the the last 10 to 20 years," he said. "That's the common story. There are no laws against it, and there are no disincentives for it."

Interestingly, the CEO inequality gap also appears within the ranks of chief execs. The study found that female and minority CEOs held far less in their retirement accounts than white male CEOs, a trend that Klinger said was "the biggest surprise."

"My first reaction was, 'Oh, I bet the men have worked at the companies longer,'" he said. "But when I saw the women actually had longer tenures, that raised my eyebrows."

One reason could be the gender gap in pay, which could extend to the executive suite, as well as the tendency for men to negotiate pay packages, while women are more reticent to do so.