How the Strategic Petroleum Reserve Works

The Strategic Petroleum Reserve (SPR) is the world’s largest crude oil stockpile, built after the 1973 OAPEC embargo to insulate the United States from import shocks. It holds roughly 714 million barrels - about 10% of annual U.S. consumption - and has been used frequently as a policy tool, including recent releases totaling about 120 million barrels. Public debate has centered on how much oil can safely be withdrawn; claims of a 300 million-barrel minimum lack firm backing, but the design of the reserve - underground salt caverns and pressure-limited storage - does set concrete limits on how much and how often it can be drawn down.

Storage was chosen as solution-mined caverns in Gulf Coast salt domes because rock salt is largely impermeable. Construction began after the 1975 Energy Policy and Conservation Act and proceeded in three phases across multiple Texas and Louisiana sites; Phase I converted existing caverns to provide about 248 million barrels, Phase II added about 290 million, and Phase III (Big Hill) pushed capacity toward the originally envisioned 750-1,000 million barrels. Building the reserve faced steep technical, environmental, and managerial challenges: inexperienced federal oversight, contractor fraud and theft, brine-disposal fights with fishermen that forced longer pipelines, and unexpected cavern pressure limits that reduced Phase I capacity by 87 million barrels and complicated the much larger Phase II caverns.