(Bloomberg) -- Exxon Mobil Corp. had the outlook on its top-notch debt rating lowered by Moody’s Investors Service Inc. to negative due to a “substantial” cash burn to fund growth.

The oil major’s credit metrics will probably weaken over the next few years as it pursues a rebuild of its upstream portfolio, as well as new chemical facilities and refinery upgrades, Moody’s said in a statement Tuesday. The outlook on its Aaa rating was reduced from stable.

“ExxonMobil’s negative outlook reflects the company’s substantial negative free cash flow and expected reliance on debt to fund its large growth capital spending program,” Peter Speer, a senior vice president at Moody’s, said in the statement. Debt will likely rise despite asset sales, he said.

Over the past 10 quarters, Exxon has frequently spent more cash on its operations and dividends than it generated as it ramps up mega projects from Guyana to Mozambique. Chief Executive Officer Darren Woods says now is a good time to be investing while rivals are retreating. But investors are wary, with the stock underperforming rivals over the past five years.

“The company’s high level of growth capital investments cannot be funded with operating cash flow and asset sales at projected levels given ExxonMobil’s substantial dividend payout,” Moody’s said.

During the 2016 oil price crash, S&P Global Inc. stripped Exxon of its highest AAA credit rating for the first time in the producer’s history, cutting it by one notch to AA+.

“The rating continues to be a reflection of the company’s consistent and prudent approach to financial management through a full range of business cycles,” a representative for Exxon said in an emailed statement.

To contact the reporter on this story: Kevin Crowley in Houston at kcrowley1@bloomberg.net

To contact the editors responsible for this story: Simon Casey at scasey4@bloomberg.net, Carlos Caminada, Dan Reichl

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