Five-year results from three batteries of evapotranspirometers located at three different places of State of São Paulo plateau were used to verify the Thornthwaite, Fenman-Bavel and Blaney & Criddle formulas for computing the potential evapotranspiration in their latitude and climatic conditions. The tanks used in the evapotranspirometers were commercial, square-shaped asbestos-cement boxes with 0.54 m² surface area. Bahiagrass (Paspalum nota turn Flügge) was planted inside and outside the tanks so that their surface plant cover represented a sample of the entire vegetated area. The tanks, or lisimeters, allow estimating the potential evapotranspiration by difference between the ammount of water added to them every two days as irrigation plus eventual rainfall, and the water leaving the tanks by percolation. Under the conditions of the State of São Paulo plateau the potential evapotranspiration data in the summer months are about twice those of the winter months. Normally the monthly value amounts to 120 mm in January but does not reach 60 mm in July. The monthly potential evapotranspiration data were correlated to those computed with Thornthwaite and Blaney & Criddle equations, the Penman-Bavel nomogram and a form of the Blaney & Criddle equation adopted to the State of São Paulo envirommental conditions. Very high correlations between measured and computed results were found. The poorest correlations were found with the Penman-Bavel method data. The: correlation coefficient (r) between computed and measured monthly results at Campinas were the following: Thornthwaite, r=0,95; Blaney & Criddte original equation, r=0,93; Penman according to Bavel nomogram, r=0,89. High accuracy or agreement between the calculated and the measured values was obtained with the Thornthwaite, the modified Blaney & Criddle and the Penman-Bavel methods. The original Blaney & Criddle equation gave very discrepant results with measured ones particularly during the winter months, whose values were highly overestimated. The Penman-Bavel method underestimated moderately the summer values, particularly at the Pindamonhangaba and Ribeirão Prêto conditions. On the other hand, the computed potential evapotranspirotion data obtained by the Thornthwaite and the modified Blaney & Criddle methods were slightly understimated at the Pindamonhangaba and Ribeirão Prêto areas but overestimated at Campinas. Both methods, the Thornthwaite and the modified Blaney & Criddle, gave practically similar results, very close to those measured, for the three localities of the State of São Paulo plateau. As computing work with both methods may be easily and quickly made, they are useful for estimating potential evapotranspiration, when numerous determinations are needed. The Thornthwaite formula has the advantage of its universal application, being indicated in the climatologic works. The modified Blaney & Criddle equation, due to its high simplicity may be useful particularly for local studies where tests approved it, like at state of São Paulo plateau. Special tables containing data for the south hemisphere conditions, and adapted nomograms using millimeter and centigrade scales were prepared and presented in this paper to facilitate computing potential evapotranspiration with the four methods studied.