On May11, 2015, WLF asked the U.S. Supreme Court to review an appeals court decision that adopted a confusing test for determining hazardous-discharge liability under the Clean Water Act (CWA). The dispute arises from the 2010 explosion on the Deepwater Horizon and the resulting oil spill in the Gulf of Mexico. In its brief in support of certiorari, WLF argued that the Fifth Circuit’s two internally inconsistent opinions finding BP liable for the spill implicitly confirm that the CWA’s “from-which-oil-is-discharged” provision is ambiguous. Such ambiguity in a harsh penal statute like the CWA, WLF contended, invites application of the venerable rule of lenity, which requires that all ambiguities in civil-penalty statutes be resolved in favor of the defendant. Instead, the panel’s interpretation of the CWA essentially ignored the rule of lenity, leading the court to interpret the CWA expansively rather than narrowly.