The correct estimation of ET in the water balance equation allows for improved water management in rice cultivation. Eight evapotranspiration estimation methods (Penman, Penman-Monteith, Pan Evaporation, Kimberly-Penman, Priestley-Taylor, Hargreaves, Samani-Hargreaves and Blaney-Criddle) were tested with 30 years of daily data, in the west coast of peninsular Malaysia. The evapotranspiration estimates by all methods shows the same trend throughout the year. Samani-Hargreaves gives the highest estimates followed by the Priestley-Taylor and Hargreaves methods. The lowest estimates were by Penman-Monteith and followed by the Blaney-Criddle and Pan methods.The Penman-Monteith, Blaney-Criddle and Pan methods estimate lower values of evapotranspiration with no significant difference among them (P = 0.05). All the other methods are significantly different from these three methods. Penman method, though is different from the three methods, estimates reference evapotranspiration close to these three methods. The Penman-Monteith, Blaney-Criddle and Pan are the best methods to estimate evapotranspiration in the study area. The Penman method can be used to get somewhat reasonable estimates though it overestimates the evapotranspiration a little. All other methods, which tend to over estimate evapotranspiration were not suitable. Comparisons of the selected methods against the Penman-Monteith method showed that they have good correlation. The Pan, BlaneyCriddle and Penman gave correlation coefficients 0.87, 0.55 and 0.97 respectively. A simple correlation equation, developed using 30-year daily data, showed that direct measurement of net radiation can be used to estimate reference evapotranspiration with considerable accuracy (r2 = 0.97)
