This paper assesses future electricity generation portfolios in Thailand in 2030 given uncertain future fossil-fuel prices, carbon pricing policies, electricity demand, and capital costs. Thailand faces challenges for generation investment given its rapid socio-economic progress and fast growing demand. A novel generation investment and planning decision-support tool which incorporates a Monte Carlo extension to conventional optimal generation mix methods combined with portfolio-based analysis techniques, is used. The tool can formally assess tradeoffs between expected future generation costs, cost uncertainties, and CO2 emissions for the range of different generation portfolios. Results highlight that different levels of future carbon pricing will have significant impacts on the most appropriate generation portfolios. The impact of carbon pricing, however, is not on the appropriate proportion of combined cycle gas turbines (CCGT) in the mix but, instead, on the future role of coal versus nuclear in Thailand. Compared with the current proposed 2030 generation mix, it is possible that there are other generation portfolios that offer lower expected costs, cost uncertainty, and CO2 emissions depending on future carbon pricing. Results suggest that this investment decision-support approach may have value for electric utilities and policy-makers contemplating significant generation investments under high future uncertainty and conflicting policy objectives. (C) 2012 Elsevier Ltd. All rights reserved.