This article considers the role of efficiencies in the context of horizontal merger review in the US, European Union and Australia. The analysis concludes that while the merger regimes in each of the three jurisdictions contemplate that efficiencies arising from a proposed merger might offset or mitigate any identified anticompetitive risks, such efficiencies claims are viewed with a high degree of scepticism by competition authorities, effectively requiring a higher evidentiary threshold be satisfied to rely on such claims. It is argued there is a deviation between the role of efficiencies contemplated in merger guidelines and how they are assessed in practice, which may inadvertently lead to type-1 errors on the part of the competition authorities reviewing a merger. Accordingly, it is suggested that efficiencies should be considered concurrently to any competition risks to allow for a more holistic merger review. In particular, it is noted that Australia is presented with an opportunity to revisit the role of efficiencies in merger review, given the current discussion around merger law reform.