The study analyzes the impact of voluntary synergy disclosures at the M&A announcement on M&A transactions in the European as well as in the US energy sector. Thereby, not only is the capital market perspective considered on both a long- and short-term horizon, but the operational point of view is also taken into account. The author shows, while utilizing the event study methodology, that capital markets attribute increased returns to those M&A transactions which expect synergy gains for both the US and European market. As the post-merger accounting study confirms the realization of these...