This paper presents a transmission planning methodology that takes explicit account of the uncertainties associated with the location and size of new generating power stations in order to produce least-cost and robust transmission expansion plans. Additionally, the planning process involves a rigorous analysis of the economics of the resulting transmission plans. The paper describes the advantages, disadvantages, and difficulties associated with the initial application of this novel approach to plan the expansion of the transmission system in two Latin American countries. The ultimate objective of the analysis was to support the broader process of securing project financing by these countries from the multi-lateral financial community.