Uruguay is in the midst of making critical decisions affecting the design of its future energy supply system. Momentum for change is expected to come from several directions, including recent and foreseeable upgrades and modifications to energy conversion facilities, the importation of natural gas from Argentina, the possibility for a stronger interconnection of regional electricity systems, the country's membership in MERCOSUR, and the potential for energy sector reforms by the Government of Uruguay. The objective of this study is to analyze the effects of several fuel diversification strategies on Uruguay's energy supply system. The analysis pays special attention to fuel substitution trends due to potential imports of natural gas via a gas pipeline from Argentina and increasing electricity ties with neighboring countries. The Government of Uruguay has contracted with Argonne National Laboratory (ANL) to study several energy development scenarios with the support of several Uruguayan institutions. Specifically, ANL was asked to conduct a detailed energy supply and demand analysis, develop energy demand projections based on an analysis of past energy demand patterns with support from local institutions, evaluate the effects of potential natural gas imports and electricity exchanges, and determine the market penetration of natural gas under various scenarios.