It's worth pointing out that these are stored across ~60 salt caverns that were built to do a max of 5 drawdowns. All of them are now at about 9 drawdowns and there's every drawdown introduces serious structural integrity issues. We will never be able to completely empty them but the actual floor is debated.

The previous head of the reserves said we "couldn't realistically go below 300m". The Dept. of Energy requires at least 250m in the reserves for emergencies. Some other have estimated we could go as low as 70m.

It's entirely possible that we've already just about reached the minimum.

The very lowest layer of oil also has more sediment mixing issues and requires more processing to be useful.