AI companies are pouring untold billions of dollars into enormous data centers in their efforts to sustain increasingly complex and resource-intensive AI models.

It’s an extremely costly undertaking built on seemingly bottomless hype — and a mountain of debt. As Japanese financial newspaper Nikkei Asia found in a recent investigation, just five US tech giants — Alphabet, Microsoft, Amazon, Meta, and Oracle — are hiding an estimated $1.65 trillion in debt that doesn’t appear on balance sheets. That’s even more than the $1.35 trillion in debt the five companies officially reported in their financial data for the most recent quarter.

Meta alone has amassed around $420 billion in off-balance-sheet debt, according to Nikkei, highlighting how precarious the AI industry’s steep investment in AI has become, and inspiring comparisons to energy company Enron, which collapsed in spectacular fashion in 2001 because of similar debts hidden behind shell companies. Like Enron, they’re using special purpose vehicles, or off-balance sheet arrangements such as legally distinct subsidiaries, as a way to make their financial reporting look healthier than it actually is — often a glaring sign that something is deeply amiss behind the scenes.

“The accounting treatment itself is in fashion,” technical accounting consultant Tom Selling told Bloomberg. “But what if one of these companies was a house of cards and was propping itself up with this accounting treatment? To me, that’s the risk.”

Experts continue to warn of an AI bubble, noting the enormous and widening gulf between company valuations and their comparatively measly profits. The latest news will do little to quiet critics who say the situation is more dire than the companies’ official balance sheets suggest.

To keep up with the ongoing AI race, tech giants are committing vast sums to build out large-scale data center projects, a long-term bet that may — or may not — pay off. They’re also selling new shares to raise new funds, as Nikkei reports, which could lead to equity dilution and a drop in investor confidence.

That could make them even more vulnerable if the AI bubble does pop, or the industry fails to generate enough demand to justify the data center construction frenzy.

The pressure is on: four of the five companies Nikkei analyzed are set to report second quarter earnings in the coming days and weeks. We’ll be watching.

More on the AI bubble: There’s a Gigantic Problem at the Heart of the AI Industry That Could Cause the Whole Thing to Collapse