A lot of people have pointed out that this event is the first time that an oil price (of any description) has turned negative.
This has been spun as an indicator of how extreme the current situation is.
It is actually, an indication of the fact that environment protection legislation has some teeth.
There have been occasions in the past (great depression for one) when assorted oil prices have headed towards negative. In those times, the solution was simple. Just set the surplus oil on fire.
At least they did not do it this time.
Omg now that you mentioned it I actually recall that happening. It wasn't that long ago actually.