Abstract The paper focuses on the forming of expectations by regulatory authorities in the case of merger control after 1973, when the German legislator stipulated a decision by its officials on future competition in relevant markets. The regulatory and decision-making behavior of officials is analyzed on the basis of selected merger procedures in the chemical industry, which underwent far-reaching structural change in the 1970s and 1980s. Here, institutionalization processes for overcoming information asymmetries and the formation of market expectations can be diagnosed inside the office as well as inside the firms. Adaptive expectations with regard to current market diagnoses and legal assumptions (“Vermutungstatbestände”) play a significant role for their forecast decisions. The study is based on previously unpublished files of the Federal Cartel Office.