[mathgenius]

It may have been ICE's crude contract, which is cash settled: https://www.theice.com/products/213/WTI-Crude-Futures

"The West Texas Intermediate Light Sweet Crude Oil futures contract is cash settled against the prevailing market price for US light sweet crude."

[whatok]

Sure, but a majority of trading was done on CME futures. In either case, you still ran into the issue of negative prices. USO only recently started explicitly stating that they would also potentially invest in ICE futures alongside CME futures.