It wasn't a trader who didn't know the price could go negative, it was a passive retail investor: https://archive.is/33zf6#selection-3201.1-3205.1 https://arch

It wasn't a trader who didn't know the price could go negative, it was a passive retail investor: https://archive.is/33zf6#selection-3201.1-3205.1 https://archive.is/33zf6#selection-3201.1-3205.1 >>>> “It didn’t occur to us” oil could go negative, A’Xiang Chen, a 26-year-old investor from Shenzhen, told Bloomberg News. https://archive.is/XBP6v#selection-2457.0-2478.0 https://archive.is/XBP6v#selection-2457.0-2478.0 >>>> Thousands of miles away, in the Chinese metropolis of Shenzhen, a 26-year-old named A’Xiang Chen watched events unfold on her phone in stunned disbelief. A few weeks earlier, she and and her boyfriend had sunk their entire nest egg of about $10,000 into a product that the state-run Bank of China dubbed Yuan You Bao, or Crude Oil Treasure. --- I guess that's exactly the part about regulation that would normally prevent people from doing these things without having full understanding of the consequences. Obviously to your point, though, it does sound like the fund managers of that fund didn't exactly have their act together, either.