https://www.energy.gov/hgeo/opr/spr-quick-facts

"The Strategic Petroleum Reserve (SPR), owned and operated by the U.S. Department of Energy, is a federally managed network of four sites located along the Gulf Coasts of Texas and Louisiana. Each site contains deep underground storage caverns carved into natural salt domes, engineered to securely hold large volumes of crude oil."

There are 61 total caverns.