CONTENTS. Introduction 2II. Substantive test - New test for the evaluation of concentrations 31. The test of dominant position and substantial lessening of competition (SLC) 42. The Green Book 63. The significant obstacle to effective competition (SIEC test) 7CRITICAL APPROACH TO THE CONTROL OF MERGER THE EU SINCE THE ADOPTION OF REGULATION 139/2004I. IntroductionIn 2004, Reg.139/2004 replaced the existing Merger Control Regulation 4064/89, thus marking a milestone in merger control in the EU. The new regulation provided for the implementation of a new type of substantial test as well as some procedural changes. Compared to the practice prior to the defeat of the Tribunal in 2002, characterized by an interventionist tendency, the Commission has demonstrated a more conservative and moderate approach. Towards the end of the 1990s, dissatisfaction with the efficiency of competition in the European Commission grew. Competition policy, especially in light of the imminent enlargement of the European Union, led to the publication of a White Paper which suggested some changes to the function and the structure of competition policy. This process, also known as the European Merger Modernization Package, ultimately led to the adoption of Council Regulation 139/2004 in early May 2004 (ECMR 04). It has been argued that the adoption of such drastic changes occurred in response to the Court's annulment of three DG Competition sanctioning decisions. In these successful appeals, the Court based its decision on the fact that DG Competition applied the criterion of proof of dominance in a very rigorous and rigid manner. Accordingly, in 2001 the European Commission published a Green Paper entitled...... middle of paper ......ies, recital 29 of the new EUMR highlights their importance in the assessment of merger control as a defense against mergers that might otherwise present competition problems. To define the impact of a concentration on competition in the common market, it is appropriate to consider the possible efficiencies claimed by interested parties which could offset the negative effects of the concentration on competition, and in particular the potential harm to consumers. If efficiencies strike a balance between the “positive” and “negative” effects of a merger, the merger may therefore not significantly impede effective competition, in the common market or in a substantial part of it. To this end, the Commission should clarify the circumstances in which it can take efficiencies into account when determining the adverse effects of an operation.