The work examines the paradigm shift in the substantive test of EU merger control from a form-based dominance test to the effects-based SIEC test and analyses the resulting increase in information requirements. Its central thesis is that the „more economic approach" creates tension with the European Commission's administrative ex ante control, as complex economic forecasts must be made under conditions of uncertainty and information asymmetry. Methodologically, the study draws on law-and-economics considerations, particularly regarding the steering of information requirements and the allocation of error costs. It shows that information deficits can be addressed through various control mechanisms: the design of substantive rules (rules vs. standards), the authority's generation of knowledge in proceedings, the scope of judicial review, and the determination of standards and burdens of proof. At the same time, it becomes clear that the shift to the SIEC test increases substantive accuracy but also entails significant administrative costs and uncertainties. The Commission's extensive investigative practice and the case law of the EU courts on standards and burdens of proof are assessed critically. The study further demonstrates that the steering of information requirements is subject to legal limits. In particular, the principle of proportionality, the requirement of expedition, and the parties' rights of defence impose normative constraints on the authority's collection and processing of information.