How can we explain institutional reforms that redistribute institutional power between the parliamentary majority and minority? This paper proposes an informal theoretical model to explain such reforms in European parliaments based on congressional literature and inductive explanations from case studies. The article argues that political parties as the relevant actors pursue institutional reforms based on their substantive goals, their current and expected future government status, transaction and audience costs of reforms, second-order institutions that regulate the relative influence of actors in changing parliamentary rules, and the institutional status quo. Hypotheses derived from this model are tested with a qualitative case study of all standing order reforms in the Austrian parliament from 1945 to 2014. The empirical analysis finds support for various hypotheses and their underlying causal mechanisms. As Austria constitutes a least-likely case, the evidence provides strong support for the theoretical model.