What's the recovery rate of the SPR?
LOL an interesting question, since it is going into an underground deposit, and there is no way to tell "exactly" how much is in there.
In fact there was a big scandal back in the 80's--many million barrels actually went unaccounted for.
You are correct to be waving the red flag.
.The SPR management office is located in New Orleans, Louisiana.
The reserve is stored at four sites on the Gulf of Mexico, each located near a major center of petrochemical refining and processing. Each site contains a number of artificial caverns created in salt domes below the surface.
Individual caverns within a site can be up to 1000 m below the surface, average dimensions are 60 m wide and 600 m deep, and capacity ranges from 6 to 37 million barrels (1 to 4.3 million m³). Almost $4 billion was spent on the facilities. The decision to store in caverns was taken to reduce costs; the Dept. of Energy claims it is roughly 10 times cheaper to store oil below surface with the added advantages of no leaks and a constant natural churn of the oil due to a temperature gradient in the caverns. The caverns were created by drilling down and then dissolving the salt with water
Wikipedia