In June 2015, the WCO News published an article about the role played by customs laboratories around the world. It focused on the evolution of laboratories in the last two centuries and explains why this role is scarcely known by citizens and the scientific community. One year later, in June 2016, during the Dutch European Union (EU) Presidency, Amsterdam held the 6th Seminar of European Customs Chemists, Sharing knowledge beyond borders. This paper provides a brief overview of customs laboratories, and then describes one of the most notable frauds discussed during the seminar due to its significant fiscal impact on many EU countries, and because it relates to several aspects of customs activity, such as economic security, policy, science and law. The case study concerns the mineral oil sector and is an example of a cross-border crime that can be detected by Customs when they have the scientific support provided by customs laboratories experienced in classification, counterfeiting activities and the investigation of fraud.