The U.S. energy sector (XLE) is facing $370 billion of debt, a number that has more than doubled in the past decade. But even as oil rebounds off 13-year lows, many energy companies are struggling to stay afloat.

To simply make the interest payments on the debt, energy companies shelled out $16.7 billion last year—about half of their total operating profit, according to data compiled by FactSet and Yahoo Finance.

The figures from the past quarter are increasingly grim: over 86% of energy sector operating profits were used to cover the interest payments on debt.

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“Servicing debt is a huge component right now, which is why they need a higher oil price,” said Dan Dicker, President of MercBloc. “But even if they were able to service…the question becomes how will they be able to raise capital when these notes come due?”

While $5.1 billion of U.S. energy debt matures this year, $25.1 billion will mature in 2017. The number risies to $52.5 billion in 2020.

“There’s not a lot of this debt that comes due in 2016. But in 2017—that’s when the rubber will really hit the road. Now a lot of these companies are already looking to bankruptcy because people know that the bond position is untenable,” said Dicker.

Energy Debt Maturity By Year, Source: FactSet More

Currently 70% of oil and gas producers have bond ratings below investment grade, according to S&P and FactSet. Last year, debt defaults topped 100, a level not seen since the financial crisis, with energy companies accounting for about one-third of the total.

Even the recent rise in oil prices won’t be enough to repair the damage for many energy companies, notes Michael Cohen, head of energy commodities research at Barclays. “The leverage at these prices is in the 7 to 9 range, so even prices going back up to $50 or $60 is not going to help that immensely,” Cohen said.

On Monday, SandRidge Energy filed for bankruptcy with $4.1 billion in debt, the fifth energy company to file for bankruptcy in the past week. Since the start of 2015, over 50 oil and gas producers have gone bankrupt, and the situation is dire for hundreds more companies, according to Deloitte.

"[Oil’s recent rise] is not enough," said Dicker. "You can’t find the financing to keep the lights on at $50 oil. Most of these guys won’t be able to keep the lights on at $65 or $70 oil."