Climate change mitigation is the key policy context for considering the role of fossil fuels in the South African energy system in the long term, so the study focuses on the impact on the energy system of an economy-wide carbon constraint, and on the role of gas within it. Since South Africa is a coal-intensive economy, substitution of gas for coal use has a potentially significant mitigation impact; in addition to this, gas complements renewable energy sources in the electricity system, because of its flexibility and so could increase the speed at which the electricity system is able to shift from a coal-centric system to a low-carbon one. Furthermore, availability of gas gives rise to mitigation opportunities in the industrial and commercial sectors via co-generation and tri-generation, both of which have overall efficiencies far higher than centralized gas power generation. The aim of the study is to provide a map of the potential for gas utilization over the long term in the South African energy system.