Corporate debt is at new highs, and these companies owe the most

• Utilities, energy firms and materials companies have taken on debt faster than they've added to earnings.
• Over the last decade, total annual EBITDA for the S&P 500 as a whole rose and then flattened, while debt issuance has continued to take off in recent years.

Corporate debt hit new highs in 2016, even as earnings grew at a slower pace. The gradual increase in debt in recent years has attracted attention because the ratio of debt to corporate earnings usually peaks during economic downturns, not during economic expansions.

That imbalance, which has led some investors to worry about the health of the market, is not spread evenly across all companies. Much of the debt accumulation relative to earnings has taken place in a few industries, according to an analysis by CNBC.

Over the last decade, total annual EBITDA for the S&P 500 as a whole rose and then flattened, while debt issuance has continued to take off in recent years. That means that the net debt over EBITDA ratio, or how many years it would take to pay off that corporate debt, has been driven up.

Much of that discrepancy between debt and earnings has been caused by utilities such as Dominion Resources and Duke Energy, which have collectively piled on $7 in debt for every dollar in annual earnings gained, largely over the last two years. Materials companies like Ball Corp. and Freeport-McMoRan have also added more net debt than new earnings, and energy companies like Chevron, Halliburton and Marathon have as a group added debt and lost EBITDA.

If we remove those three sectors from the S&P 500's overall ratio, the rest of the index has a slightly lower ratio of debt to earnings than it did a decade ago.

Investors know about the debt that has been piling up in the energy sector — hundreds of such companies went bankrupt in recent years as oil prices weakened, leaving billions of dollars in debt in question. Even with crude prices recovering some, many companies remain weighed down by debt.

The market's debt binge may not be as widespread as some commentators have suggested, but there are number of companies outside those sectors that have also seen their debt ratios rise in recent years. About two-thirds of companies in the Dow 30 have higher ratios than they did a year ago, even if companies like Microsoft, Johnson & Johnson and Cisco have canceled out those increases in the Dow index overall by paying off what they owe and increasing their earnings.

Companies including Caterpillar, Chevron and McDonald's have all increased their net debt by a year's worth of EBITDA or more since 2006. It's difficult to know how much debt is too much debt, but we may have the opportunity to find out soon, as the Federal Reserve raises interest rates or if the market enters a downturn.

Companies that have loaded up with historically high debt levels — especially in the energy and utilities sectors — could be squeezed by their financial obligations.