Oil and gas exporting countries have long been conscious of the need to prepare for a future when resources would be exhausted. Shifting from being mere exporters of crude oil to integrating downstream and diversify their economies has been a proclaimed strategy of many of these countries for decades. Yet, downstream diversification has been a winning strategy for very few oil and gas exporters, and even these have pursued other alternatives, notably establishing large sovereign wealth funds, with greater vigour. Several important oil and gas exporting countries have failed to either diversify downstream or establish large sovereign wealth funds, and remain heavily dependent on exporting raw hydrocarbons. Their future economic viability in a world that is bound to reduce its reliance on fossil fuels is seriously threatened. This chapter describes the challenges faced by oil and gas producers with respect to downstream diversification, and draws lessons for mineral producers.