Shale gas policies vary significantly across Europe, notably in Russia-dependent Central Eastern Europe. Most strikingly, Bulgaria banned shale gas, whereas Poland remains firmly committed to fostering it despite its drawbacks. This article uses a policy regime approach to explain the shale gas puzzle. Drawing on a large set of interviews, the piece investigates regime strength as the causal factor that explains the adoption of specific shale gas laws (Poland) or a fracking ban (Bulgaria). It finds that the Polish shale gas policy regime was strong, based on a powerful political narrative and characterized by an institutional process ensuring the buy-in of actors from relevant policy levels and subsystems. In Bulgaria the policy regime was weak, failed to co–opt key stakeholders, and was institutionally ill-designed. The findings show how different degrees of policy regime strength translate into diverging policy trajectories in two countries that otherwise operate in similar environments.