For decades, employment-based health insurance coverage has been going in one direction: down.

In 2011, slightly more than 58% of the population had employment-based coverage, a nearly 10 percentage point drop compared with 1999, according to U.S. Census Bureau statistics.

Retiree health care coverage has fallen sharply as well. Last year, just 17% of employers with at least 500 employees offered health care coverage to Medicare-eligible retired workers, down from 40% in 1993, according to a recent Mercer L.L.C. survey.

The main reason for the decline in employer group medical coverage is not complex: The cost of health care coverage has soared. In 2010, the most recent year statistics are available, health care expenditures neared $2.6 trillion, a 10-fold increase compared with $256 billion in 1980, according to the U.S. Department of Health and Human Services.

Correspondingly, the cost of employer-sponsored health care plans has jumped. In 2012, group health care costs averaged $10,558 per employee, a roughly $3,500 per employee increase in just seven years, according to Mercer.

Several factors have inflated costs. For retiree health care plans, increased longevity has been a big cost driver. With people living longer, employers with plans offered to Medicare-eligible retirees face far greater costs than employers could have anticipated when they set up the plans decades ago.

“Employers look at the cost of providing insurance to retirees living longer” and increasingly realize it is a cost that is not sustainable, said Rob Panepinto, managing director of the exchange solution division at Connextions Inc. in Orlando, Fla.

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Other well-known factors driving up costs include the availability and growth of expensive medical procedures and costly prescription drugs.

Trying to manage soaring costs and administer their health care plans has been especially challenging for corporate benefits managers, as tough economic times forced employers to try to do more with fewer resources.

And as health care costs continue to climb and employers try to shift at least a portion of the increasing cost burden onto plan participants, that effort has not, unsurprisingly, been welcomed by those participants. Twenty percent of employees responding to a 2012 Mercer survey said their health care benefits were “probably” or “definitely” not worth the associated out-of-pocket costs, compared with 15% a year earlier.

Those continuing cost increases, along with fewer corporate resources to battle those rising costs and administer health care plans, are problems few employers see going away.

But it is an issue they have little choice but to try to tackle.

“Health care costs are such a big number that corporations have to think about it,” said Greg Besio, executive vice president and chief human resources officer at Aon P.L.C. in London.

Indeed, employers and their advisers are intensely examining the problems — especially costs — associated with offering health care plans.

On the retiree health side, employers have begun to question the logic of offering just one or two plans.

“There was no choice. It was one-size fits all,” said Al Rapp, corporate health care manager at United Parcel Service Inc. in Atlanta.

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Indeed, with that “one-size-fits-all approach” some employees or retirees can end up with far more or far less coverage appropriate for their individual needs, experts say.

But if employers were to add many more plan choices, they would lack the resources to explain those choices to their employees and retirees, as well as to administer the plans.

At the same time, the predominate way health care plan coverage is funded — employers paying a fixed percentage, often between 70% and 80% of plans premiums, and employees or retirees picking up the remaining share — also is a problem.

In situations often pervasive among large organizations, when employers self-fund their health care plans, employers face unpredictable and potentially huge costs from catastrophic claims, such as from premature births.

But the picture is far from all gloom and doom. In 2012, group health care costs rose an average of 4.1%, the smallest annual increase in the last 15 years, according to Mercer.

Indeed, hammered by big and continued cost increases, employers are finally starting to take action to try to control those increases

In the last few years, for example, many employers have revamped their health care plans to give employees financial incentives to take better care of their health.

And now some are exploring and in a growing number of cases entering the latest and potentially one of the most promising ways to continue to offer coverage, while still holding down costs: private health insurance exchanges.

Health insurance exchanges are the “path of the future” for many large employers, said Greg Besio, executive vice president and chief human resources officer at Aon P.L.C. in London.