(Bloomberg) — In the months after Sept. 11, 2001, as U.S. security officials assessed the top targets for potential terrorist attacks, the small town of Cushing, Okla., received special attention. Even though it is home to fewer than 10,000 people, Cushing is the largest commercial oil storage hub in North America, second only in size to the U.S. government's Strategic Petroleum Reserve. The small town's giant tanks, some big enough to fit a Boeing 747 jet inside, were filled with around 10 million barrels of crude at the time, an obvious target for someone looking to disrupt America's economy and energy supply.

The FBI, state and local law enforcement and emergency officials, and the energy companies that own the tanks formed a group called the Safety Alliance of Cushing. Soon, guards took up posts along the perimeter of storage facilities and newly installed cameras kept constant surveillance. References to the giant tanks and pipelines were removed from the Cushing Chamber of Commerce website. In 2004, the Safety Alliance simulated a series of emergencies: an explosion, a fire, a hostage situation.

After the shale boom added millions of additional barrels to Cushing, its tanks swelled to a peak hoard of more than 60 million barrels this spring. That's about as much petroleum as the U.S. uses in three days, and it's more than six times the quantity that triggered security concerns after Sept. 11. The Safety Alliance has remained vigilant, even staging tornado simulations after a few close calls.