Oil leaks from aboveground tanks have contaminated soil and water, threatening human health and wildlife. To prevent damage from oil spills, the Environmental Protection Agency (EPA) issued the Spill Prevention, Control, and Countermeasure (SPCC) rule in 1973. EPA’s 10 regions inspect oil storage facilities to ensure compliance with the rule. EPA estimates that about 571,000 facilities are subject to this rule. Some states also regulate oil storage tanks. GAO determined (1) how EPA regions implement the SPCC program, (2) the data EPA has to implement and evaluate the program, and (3) whether some states’ tank programs suggest ways for EPA to improve its program. GAO surveyed all 10 EPA regions and interviewed officials in EPA and six states selected on the basis of experts’ recommendations, among other criteria.