Oil regimes have undergone a momentous transformation over the past 50 years. While the Arab OPEC nationalizations captured the world’s attention, the parallel introduction of Indonesia’s production sharing agreement (PSA) has produced a shift in ownership and control of oil in nearly half of the world. Contrary to popular narratives about the oil industry that privilege the coercive power of home countries and international oil companies, I argue that the transformation of oil regimes has been led by the developing world. Lacking significant power asymmetries and perceiving similarities of interests, the states of the South have learned from each other’s experiences. As prominent developing countries have joined the ranks of PSA-users, prestige-seeking emulation has supplemented learning in driving diffusion. This argument is developed through a two-level theoretical model. At the international level, it assesses how the distribution of power and peer groups affect the relative influence of coercion, competition, learning, and emulation. At the domestic level, it incorporates elite orientation to determine a state’s receptiveness to diffusion by different means and sources. Applying this model to the diffusion of oil regimes, I argue that the success of the PSA, as an innovation of the South, is driven primarily by learning and emulation. I test this argument using a multi-method research design that combines quantitative analysis of an original dataset of petroleum regimes with qualitative evidence from U.S. government archives and interviews with senior industry experts. The diffusion of the PSA is not just substantively but theoretically significant. The PSA has not only been widely adopted in the developing world, but is an innovation of the South, making it a true case of South-South diffusion. Given the Northern bias of the diffusion literature, the finding that this form of diffusion can be highly successful in an area of strategic significance to the rest of the world is indicative of the need to expand research on South-South diffusion. The argument advancing the centrality of learning and emulation is also significant to the oil literature, which has traditionally placed coercion at the center of policy-making.