Fortune 1000 companies have amassed nearly $300 billion in retiree health care plan obligations, with a majority of those employers not funding those obligations, according to a new analysis.

Fortune 1000 companies reported $285 billion in retiree health care plan liabilities at the end of 2013, according to a Towers Watson & Co. analysis of those employers' financial disclosures filed with the U.S. Securities and Exchange Commission.

Of the 501 companies with retiree health care plan obligations, just over two-thirds, or 67%, had not funded any of those obligations, while just 13%, or 68, of the employers had funded up to 33.3% of the liabilities.

At the other end of the funding spectrum, just 4%, or 19, employers had fully funded the liabilities, while 8%, or 40, employers had funded at least two-thirds of the liabilities, and the same number and percentage had funded between one-third and two-thirds of the obligations, according to the analysis, which was released Monday.

Typically, those liabilities stem from retiree health care plans set up decades ago, as few employers now offer the coverage to new employees.

The paltry funding of retiree health care plan obligations is in big contrast to the funding of pension plan liabilities. For example, at the end of 2013, the 100 largest pension programs sponsored by publicly held employers were on average 91.2% funded, according to an earlier Towers Watson analysis.

The chief reason for the huge disparity in the funding levels of corporate retiree health and pension plans is that while there are federal funding requirements for pension plans, there is no such mandate for retiree health care liabilities.

Still, some employers have taken steps to manage or even eliminate the liability. For example, in 2007, the Big 3 automakers agreed to contribute tens of billions of dollars to special trusts known as voluntary employees' beneficiary associations in exchange for eliminating their obligation to provide retiree care benefits to current and future retirees represented by the United Auto Workers union.

Under another approach, unveiled by Towers Watson earlier this year, an employer could purchase a group annuity from an insurer, paying the full premium upfront. The insurer then would provide retirees with a monthly tax-free check, which a retiree would put toward the premium of the plan he or she selects in a Towers Watson private insurance exchange.

“Companies can end the obligation without creating adverse consequences for themselves or their retirees,” Mitchell Cole, a Towers Watson managing director in Stamford, Connecticut, said in a statement.