Most of the theoretical and empirical literature on bank margins has dealt solely with interest margins. Applying the seminal Ho–Saunders model (JFQA, 1981) to a multi-output framework, we show that the relationship between bank margins and market power varies significantly across bank specializations. In this context, European banks are a better laboratory than US banks, since they have generally enjoyed a more flexible regulatory environment in which to provide a wider range of services. Using accounting margins and New Empirical Industrial Organization margins, we find that market power increases as output becomes more diversified towards non-traditional activities in European banking.