Much has changed since the establishment of the Strategic Petroleum Reserve in 1975, and the American Association of Petroleum Geologists (AAPG) explores what these changes mean in its "Spheres of Influence" publication. The initial thought was that there would be few large drawdowns from the reserve, but what has actually happened has been several smaller drawdowns. Read about how this, and the changing geology of the salt caves used to store the crude, highlights a mismatch between the initial policy and the reality of how the reserve is used.