Mergers and acquisitions are considered effective means to enter a new market or improve a weak market position. Despite numerous failed M&A transactions in recent years that have led to significant value destruction, there is a lack of theoretically grounded options for action in post-merger integration (PMI) within business and social science research. Jürgen F. Studt qualitatively and quantitatively examines whether and to what extent a change management approach can be theoretically substantiated and how the sustainability of an approach in PMI—and beyond—can be achieved. The case study focuses on the acquisition of Veba Oel and Aral by BP, which he accompanied as the head of the integration team. He demonstrates that employees of companies that prioritize brand and market leadership before the merger are affected by PMI.