Between 2003 and 2007 six regional statutes of autonomy were reformed in Spain. These are Organic Laws that form part of the 'constitutional bloc' in Spain and determine the characteristics of state decentralization, so contain high thresholds for revision in the regional and Spanish parliament. Statutes are a flexible component of 'non-institutional federalism' in Spain and their negotiation highlights both centripetal and centrifugal dynamics in state design. Existing empirical studies have compared the content of these reforms. This article compares the political dynamics of statute reform, in light of existing literature on coalitional bargaining. It argues that statute reform is a competitive two-level game (regional and central), which requires parties to form single-issue 'statute coalitions'. Statute coalitions require varying degrees of inter-party co-operation, and can distort more permanent governing or parliamentary coalitions between statewide and non-statewide parties. They can exacerbate intra-party tensions, but may also be useful for 'coalitional experimentation' in multi-level arenas. Statute negotiations are unbounded because Spanish parties exploit them for electoral advantage and not merely to secure their policy preferences. This article contains two case studies of statute reform (Catalonia, Valencia) which illustrate these complex and varied dynamics, and suggests comparative avenues for further research on constitutional reform in multi-level systems.