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Recently governments and universities in many South American countries have shown considerable interest in a planned and orderly development of available water resources. A case in point is the preliminary study reported in which the problem is approached by utilizing a general mathematical model of the hydrologic system. Specifically, the study involves simulation by means of an electronic analog computer of the hydrology of the Paez-Pedraza region of south western Venezuela. The various processes within the model are linked by the continuity-of-mass principle, which requires a hydrologic balance at all points. The analog computer is ideally suited to the solution of the time-dependent differential equations of the model, and to the trial and error process required during testing and verification. Despite restrictions imposed by data limitations, a satisfactory model based on a monthly time increment is proposed. The model is applied for (a) estimating runoff from ungaged subbasins, (b) testing the sensitivity of the system to certain parameters and processes, and (c) providing insight into data requirements within the region. In addition, the study provides a basis for evaluating the feasibility of conducting further and more detailed investigations of the Paez-Pedraza and other areas of Venezuela. Several recommendations for additional research are presented.