Australia's energy system faces a number of environmental challenges and chief among them is reducing greenhouse gas emissions. In the electricity sector, the Australian government has began implementing policies, which require greater use of gas and renewables based technologies. In this study, we simulate the optimal shares of several electricity generation technologies for Australia under a policy of greenhouse gas mitigation. In doing so, we seek to determine the likely technological investment paths over the next two decades and consider the sensitivity of those projections to assumptions regarding technological change, resource scarcity and economies or diseconomies of scale.