Uniformity in the treatment of environmental violators helps achieve the system’s goals of deterrence and fairness. In 1984, the Environmental Protection Agency (EPA) adopted a general penalty policy that sought to promote uniformity in federal environmental enforcement while still providing necessary discretion to account for individual circumstances. However, the EPA then delegated most of the enforcement of these laws to the states, which have a wide range of statutory penalty authorizations. Even when the EPA takes the lead, regional offices use penalty policies that allow a remarkable degree of discretion, creating significant potential for disparate treatment. This study is the first to analyze data from the EPA’s public database to determine whether this potential has resulted in actual significant penalty disparity. Data from the last 10 years indicates that the EPA is not achieving its uniformity goals. Significant disparities exist in the median penalties imposed from state to state, between the states and the EPA, and among the various EPA regional offices. We recommend changes to the EPA’s delegation regulation and to its penalty policies to reduce this disparity and the potential for unfairness.