The monthly oil contract expired. So normally, folks who trade contracts like so many 1s and 0s on a computer screen would offload their contracts to physical buyers.
End of month, someone needs to take physical delivery, right?
1/
In a market w/ sellers and no/few buyers, prices fall...
2/
"I don't want to take delivery of any oil. I'm going to sell."
So $20 became $10, then $5, then 17 cents ... and then prices went negative.
3/
Physical trader: Maybe. How about you pay me $35 for every barrel I take off your hands.
4/
-endit-