Bank of China Ltd. customers learned an $85 million lesson on the perils of speculating on crude oil this week. Hundreds of angry retail investors have flooded onto the internet to protest against the lender after their investments in products linked to West Texas Intermediate were wiped out by oil’s unprecedented collapse below zero on Monday. Heaped on top of about 200 million yuan ($28 million) of initial losses is about 400 million yuan that they owe Bank of China due to the plunge into negative territory, according to people with knowledge of the matter.

The losses thrust Bank of China into the center of oil’s shocking collapse and show how retail investors have been caught up in the catastrophic crash. The lender suspended trading in the product earlier this week and has been joined by more of China’s biggest banks halting sales of similar vehicles that had become a popular way of speculating on swings in oil. A majority of the 3,700-odd customers invested in the doomed product had been betting on an increase in prices, said the people, asking not to be identified as the details are private. Irate customers are now demanding the bank shoulder some of their losses.

“In theory, these oil-linked bank funds should have their own risk management tools that prevent losses on behalf of retail investors,” said Chen Tong, an analyst at First Futures in Tianjin. “First, the fund manager should have set a ratio to liquidate the positions for investors when certain principal is lost. Second, they need to at least start rolling the contract two weeks before expiry date.”

Bank of China settled customers’ outstanding positions in its product on April 20 at minus 266.12 yuan a barrel, the lender has said. That’s roughly in line with the Monday close of minus $37.63, but not with the actual $10 that was the price when the May futures contract expired on Tuesday.

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The bank maintains that it settled the contract in accordance with guidelines previously disclosed to clients. Those include rolling over the underlying contracts the day before expiry, which for the May contract was Monday.