CONTENTSI. Introduction 2II. Substantive test - New test for the assessment of concentrations 31. The dominant position test and the substantial reduction of competition (SLC) 42. The Green Paper 63. The significant obstacle to effective competition (SIEC test) 7CRITICAL APPROACH OF MERGER CONTROL IN THE EU SINCE THE ADOPTION OF REGULATION 139/2004I. IntroductionIn 2004, Regulation 139/2004 replaced the existing Merger Control Regulation 4064/89, marking an important milestone in merger control in the EU. The new regulation provided for the implementation of a new type of substantive test as well as certain procedural changes. Compared to its practice before the defeats of the Tribunal in 2002, characterized by an interventionist tendency, the Commission demonstrated a more conservative and moderate approach. Towards the end of the 1990s, growing dissatisfaction with the effectiveness of the European Commission's competition policy, particularly in light of the imminent enlargement of the European Union, led to the publication of a white paper suggesting several changes to the function and 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 use of such radical changes was a response to the General Court's annulment of three DG Competition sanction decisions. In these successful appeals, the General Court based its decision on the grounds that DG Competition applied the standard of proof of dominance in a very strict and rigid manner. Therefore, in 2001, the European Commission published a Green Paper calling for...... in the middle of the document ......ies, recital 29 of the new EUTMR highlights their importance in the assessment of merger control as a defense against mergers that might otherwise raise competition concerns. In order to define the impact of a concentration on competition in the common market, it is appropriate to consider possible efficiency gains claimed by the interested parties which could offset the negative effects of the concentration on competition, and in particular the potential harm to consumers. If the efficiency gains result in a balance between the "positive" and "negative" effects of a concentration, then the concentration may not significantly impede effective competition, in the common market or in a substantial part of it. this one. To this end, the Commission should clarify the circumstances in which it can take into account efficiencies when determining the negative effects of a transaction..