The May 'front month futures' contract for oil has gone negative. It is now -$37 a barrel (that's negative $37). This is the futures contract that expires tomorrow, and there is a cascade effect going on - basically.

(This does not mean oil in general is -$37/barrel)

This is a decent explainer of what is going on with oil today. Note the numbers themselves are out of date. https://www.reuters.com/article/us-global-oil-contracts/expiring-us-crude-oil-futures-contract-posts-epic-40-slide-idUSKBN2221TS

Here are some numbers as of the time of writing. You can see that the June-onwards contracts for oil are trading at 'normal' levels.

Here's a good thread that also helps explain things https://twitter.com/RogerDiwan/status/1252324705291374592