Why do states exist in their present territorial form? Although there has been substantial research on sovereignty and state formation, scholars have tended to focus on the European experience or the international system as a whole. As a result, the making of non-European states, many of which are different from their European counterparts in their experience of colonial rule, have been understudied, and factors particularly relevant to them have been overlooked. This article investigates the impact of one such factor, natural resources, along with the type of colonial administration system, on the creation of states through decolonization. Focusing on arguably the most significant natural resource in the modern world, oil, I argue that when faced with a project for a merger, (1) pre-independence oil production and (2) the protectorate system enabled colonial areas to become independent separately from neighboring regions, creating states that would otherwise not exist, while the lack of either of the two conditions resulted in amalgamation with other areas. I substantiate this argument through historical within case analysis of Qatar and Bahrain based on extensive archival research, followed by comparative case studies of other colonial areas in the Persian Gulf and Borneo. This article contributes to the literature on state formation by adding a new explanatory factor and advancing the understanding of state formation in former colonies. It also contributes to the literature on the politics of natural resources by revising the existing understanding of the oil sovereignty nexus and showing that the very existence of some petrostates is contingent on oil.