Design and operation of water resources management systems in many countries, particularly in the developing world, very often suffer from inadequate hydrological data. Consequently, many water resources management projects in the Third World do not function as optimally as they are supposed to since long uninterrupted time series of data are often not available for the assessment of the performance and reliability of the projects. Besides data inaccuracy, inadequate data may comprise the total absence or incompleteness (in terms of length of records) of data or irregular observation periods, leading to a number of gaps or discontinuities in the series. Infilling of missing sections of data is often necessary prior to the practical use of hydrological time series. It was the aim of this research study to find the most effective ways of infilling the numerous missing runoff data most commonly associated with Third World data based on a simple Decision Support System (DSS) valid in West Africa.