Yes, in the strategic oil reserve there was, but not in many other oil storage facilities, and government buying processes for everything are slow and complicated. However, the negative prices aren't for oil as delivered where you want it. It is for oil coming out of a tap at a storage facility somewhere in Illinois (or rather, entering a tank that you rent in that storage facility). All of those tanks were full when oil prices went negative, and there wasn't enough demand to transport oil out of that facility. Most storage facilities were full, and new ones couldn't be built in time.