We propose a simple model of a partially integrated industry which explicitly takes into account persistent production cost differences across upstream firms, such as one might observe in natural resource industries. The model allows us to highlight the respective roles of strategic considerations in the determination of an integrated firm's interaction with the non-integrated sector of the industry and, in the end, on its relative upstream-downstream specialization. Stylized facts from the world oil industry are used to illustrate the type of behaviour one might expect in this context.