Focusing on the need for energy to sustain economic development on a long-term basis, the document examines energy options of the post-petroleum era in developing nations. Nuclear power and solar power are the most important among proposed alternative energy sources. Limited applicability of nuclear technology to the Third World is discussed. Problems include the need of most developing nations to seek foreign fuel to power nuclear plants, the difficulty of designing nuclear facilities that work equally well in different environments, and the problem of decommissioning radioactive facilities at the end of their usefulness. Energy-related research and experiments indicate that the most likely sources for new energy are solar (sunlight, wind, hydropower, and biomass). Factors which should encourage the Third World to harness solar energy sources include: a general abundance of sunlight, a dispersed and predominately rural population (which encourages decentralized energy resources), prohibitive cost of conventional energy, customary dependence on indirect solar sources such as firewood, and insignificant capital investment in petroleum-powered energy. Various objections and reservations concerned with the transition to solar energy are evaluated. The conclusion is that solar energy, the most viable energy source in the post-petroleum age, can contribute positively to economic development in both developing and industrialized nations. (Author/DB)