In my “Properties of Stock Options” lecture note, a particularly important theorem relates to the notion that derivatives (options) prices must be non-negative. Interestingly, back in April 2020, prices for oil futures contracts actually turned negative; see the Wall Street Journal article entitled “U.S. Oil Costs Less Than Zero After a Sharp Monday Selloff” (an ungated PDF version is available at https://bit.ly/oilpriceshock). Quoting from that article, “The unusually large difference in price between oil for delivery in May and later has traders filling up tankers and setting them adrift.” Basically, if you had the means to store oil in the meantime, (e.g., offshore in a very large crude carrier) it made a lot of financial sense to be paid to assume ownership of the (negatively priced) May 2020 contract, and sell a later dated futures contract at which time you could deliver the goods! Apparently, somewhere off the coast of South Africa was an especially popular place to anchor due to its relatively equidistant access to markets in Asia, Europe, and the Americas.
In closing, the following related video from wsj.com is well worth 95 seconds of everyone’s time!