When there were more sellers than buyers, the storage facility became full and because of lockdown measures there were no trucks to take the oil anywhere else to relieve the pressure.
Still, the unprecedented event has attracted scrutiny and even raised questions about the viability of some international oil benchmarks.
Ever since that day on April 20, when US crude futures collapsed and prices turned to a negative $40 per barrel, the US oil market has been looking for an alternative to Cushing.