We introduce an ecological Europeanization framework that provides the opportunity to determine the actual size of European and national rule stocks as objective measures of potential sources of external red tape drivers. We illustrate our ecological framework with the case of Dutch competition law for the period running from 1962 to 2010. Applying our framework, we infer the share of European rules in the entire national rule population, thus revealing what part of the national rule stock is Europeanized. We find that all rule stocks in our sample have increased drastically over time. Moreover, European rules have different effects at the national rule stock level, depending on rule type. European rules serve as weak substitutes for Dutch formal laws, and as complements for Dutch secondary rules. We discuss how the ecological method of measuring external law evolution may inform future organizational red tape research specifically, and studies into formalization generally.