In this paper. the past, present and future applications of the exergy concept in applied process research. development and engineering projects in the petroleum refining and petrochemical industry, conducted at the Mexican Petroleum Institute (IMP), are described. These applications are the result of a clear recognition of the challenge represented by the reduction of energy degradation, i.e. the application of the second law of thermodynamics, through the exergy concept, which allows to simultaneously consider the three E's model: energy-economy-ecology. Applications can be grouped in two complementary directions: the first, methodological, direction consists in integrating within general simulation, analysis and optimization programs, the subroutines required to conduct exergy analyses, in order to get in a quick and precise manner, all information required to integrally optimize chemical processes through detailed exergoeconomic and exergoecologic studies. The second direction refers to research and technological development of specific systems and processes, integrally optimum, of which the justification lies on the exergy analysis, i.e. on its capacity to simultaneously consider energy, economy and ecology aspects, such as diabatic distillation, absorption heat pumps, coking-gasification-combined cycle co- and tri-generation, fuel cells, etc.