The new substantive test reflects and develops the experience gained in the years of application of the old substantive test under the old Merger Regulation. It adapts the criteria for the assessment of mergers to new economic developments. There are however under the regime of the new SIEC-test some cases which were decided differently than under the old structural approach. It clarified the expressed uncertainty regarding the alleged oligopoly blindspot. It moved the appraisal criteria of mergers towards the SLC-test and therefore stepped in the direction of a global standard of merger control. It is undisputed that the new test is not a big change in merger control, albeit it seems as if a new European substantive test was developed. The largest change is the more economic (or more sophisticated) approach. The change also manifests in the reasoning of decisions, which as a result of sophisticated economic analysis increased in volume. The more economic approach reflected in the new substantive test gives the Commission wider leeway. This uncertainty created with the new test is encountered with the issuing of the horizontal and the non-horizontal Guidelines improving the efficiency, consistency and transparency of the merger review process. The discussion of the issued Guidelines however showed that there are still areas, where legal uncertainty is quite high. A very controversial topic will be the treatment of efficiencies, especially the wide discretion of the Commission and the burden of proof. Although the new test in contrast to the old appraisal criteria rendered the opportunity to consider efficiencies the Guidelines and the decisions of the Commission still have a very restrictive attitude, which makes one come to the conclusion that in practice the intended change towards a less restrictive practice did not take place. The Commission however seems to further abandon argumentations commonly described as efficiency offense. It still stays very unclear in this respect, where and when the protection of competitors is considered. Further there seems to be a fundamental misconception when applying efficiencies only if a consumer benefit can be observed. The Commission not only refuses to consider efficiencies, which are not passed on to consumers298 but also efficiencies, which would for instance take place in other markets. There does not seem to be a legal basis for this. National Austrian merger control applies a fundamentally different substantive test (structural approach), which is more oriented on the appraisal criteria preceding the SIEC-test. The implementation of such a less sophisticated approach seems for small mergers more appropriate. Choosing a structural approach by the national legislator does therefore not raise constitutional concerns.