This paper discusses the principles and applications of the GALO computer program, which generates numerical simulations of the evolution of a sedimentary basin. The program calculates variations in the sedimentary bed thickness, predicts the thermal regime in the sedimentary cover or in the basement, and estimates the potential hydrocarbon yield of the source rocks. Alternative methods for determining the magnitude of tectonic subsidence of the basement surface within the framework of a local isostasy model are applied to provide a detailed model of the sequential tectonic-thermal events involved in the development of the basin. The program determines reaction parameters controlling the maturation of the organic matter in source rocks; these parameters are based largely on the hydrocarbon pyrolysis yield data and the stage of maturation of the organic matter entered into the program. Neglecting this stage drastically displaces the reaction spectrum toward higher energies, leading to considerable underestimation of hydrocarbon output.