Though note that, for some reason, the last 250M barrels are not physically extractable from the SPR, and the red line has dropped to 284M.
Not exactly "not physically extractable", but extractable only slowly, probably contaminated by water, in a way that is very expensive to refine.
People jump over the details in normal times, but then times get abnormal and impossible things start to happen.
The red line is a percentage. Axis on the right.
Source on that? Not doubting, just curious. If true that explains the Y axis starting there.
The "for some reason" is that the caverns the oil is stored in are expected to become geologically unstable if they are emptied below a certain threshold. Extract below the 250 mark, and run the risk that they will collapse and cannot be refilled.