Headlines had oil selling at -$37.63 per barrel at close on Monday, April 20. The negative sign in front? Sellers had to pay buyers $37.63 to take the oil off their hands. Except this wasn’t the price of oil. It was the price of a useful financial instrument, called a futures contract, in this case a contract for delivery of oil in May at a particular price. The nearest futures contract in date is often used as a proxy for the price of oil, since it trades regularly and usually tracks the price of oil well. But on Monday, quirks in the futures market created an artificial price that, while historic and capturing the extreme stress we’re seeing in the oil market, was not quite the same as the actual price of oil.