Does oil hinder or improve military power? How are oil states' search for a capable and effective military conditioned by the nature, dynamics, and consequences of their political economies of oil? Despite paramount policy implications and theoretical relevance, specific conditions and causal mechanisms of this relationship remain poorly understood. Two factors are central in making sense of oil states' military capability and institutions. The geological endowment of oil determines the material potential, and the management structure of oil revenue informs the state's long-term developmental capacity, as well as the professionalization and institutionalization of its military. Accordingly, oil becomes either 'a mixed blessing' or 'a power booster' for oil states' pursuit for military power. The theory is supported by plausibility probes on two carefully selected cases-Norway and Azerbaijan. The findings reveal previously neglected paths for oil to influence the states' politics and national security.