When spot prices fall relative to futures prices, traders buy the commodity and store it until it is in greater demand. With the reduction in demand and excessive supply, storage is becoming more scarce and becoming more expensive. The more expensive the storage, the lower the spot price needs to fall before traders will buy and store the commodity. Usually, there is some customer that would be willing to buy at a low price but currently, there is no way to store the oil and very few consumers of oil due to the COVID-19 lockdown. Traders with long positions usually close their contracts and buy new contracts with a longer maturity in order to avoid taking physical delivery. With no buyers, these traders needed to unload their contracts at ridiculous prices to avoid being fined for not taking delivery at the expiration of their contracts.
Stephen Rush 