There is a widely held view that in the period since the early 1990s the European Union (EU) has overtaken the United States (US) as the leader with the most advanced or demanding environmental regulations. However, it is striking that there are very few robust comparative evaluations of the outcomes of environmental regulations or of levels of industrial environmental performance in the EU and US. This paper seeks to address this by comparing the standards and levels of performance achieved based on a case study of the regulation of a classic air pollutant (benzene) from a widespread industrial sector that has been heavily regulated in both settings for many years (oil refineries). Contrary to expectations, we find that on average normalised levels of emissions from EU refineries are three times higher than those from US refineries, and whilst outcomes in the US show marked convergence towards the best standards, there continue to be wide variations in the outcomes achieved in different EU Member States, despite the rhetoric of harmonisation.