Reference evapotranspiration (ET0) is an essential parameter for hydrological modeling, irrigation planning and for studying the impacts of climate change on water resources. The Penman-Monteith method is recommended for estimating ET0 under all climatic conditions. But its application is limited in regions where data are difficult to access. The alternative is to use methods that incorporate fewer climatic parameters. The objective of this work is to evaluate twenty alternative methods of estimating ET0 and to calibrate and validate the best ones in order to adapt them to the climatic context of the basins of Senegal, Gambia and Casamance. This tree basins are the main hydrosystems of Senegal. The KGE and the PBIAS were used to evaluate the performance of the methods. The results show that the methods of Valiantzas 1, Doorenboss & Pruitt and Penman are the most robust for the estimation of ET0 in the three basins. The calibration/validation allowed the improvement of the methods of Trabert, Valiantzas 2 and Hargreaves & Samani for the estimation of the reference evapotranspiration in the basins of Senegal, Gambia and Casamance.