Conduit OFC and sink OFC is an empirical quantitative method of classifying corporate tax havens, offshore financial centres (OFCs) and tax havens. Traditional methods for identifying tax havens analyse tax and legal structures for base erosion and profit shifting (BEPS) tools. However, this approach follows a purely quantitative approach, ignoring any taxation or legal concepts, to instead follow a big data analysis of the ownership chains of 98 million global companies. The technique gives both a method of classification and a method of understanding the relative scale – but not absolute scale – of havens/OFCs.