This is the most detailed breakdown of the reserve contents, updated weekly. the sweet/sour differential isn't listed on any other data sources for some reason, and if you want a longitudinal record you'll have to make your own.

https://www.spr.doe.gov/dir/dir.html

I think there's a statuary limit at 150 million because there must be an "emergency military reserve" but the caverns start collapsing at 70 million.