The present article characterizes economically and socially the two past centuries, focusing the consumption development of several primary-energy sources, linking it with this century's reality. The main objective is to demonstrate the relationship between the substitution process of primary-energy sources and the socio-economic development. Our analysis focuses on four technological transformations that have already occurred, emphasizing some aspects of present technological transformations. Thus, the role of primary-energy sources in the development of each long economic wave is analysed, as well as its geopolitical, commercial and social importance. Finally, bearing in mind the past dynamics associated with long structural waves, and making use of technological forecasting tools (Logistic Substitution and Delphi Technique), a future perspective is presented in which the substitution process points toward alternative-energy sources. (c) 2007 Elsevier Ltd. All rights reserved.