In this study were analised datas of evaporation from Class A pan, collected in Climatological Station, which is localized on km 14 - ZF 02 - Manaus Caracaraí Road. In that local the dominant climatic parameter in the process of pan evaporation is the saturation deficit of air, with a determination coeficient R2 = 0.91 in the equation of regression while the ratio between portencial evaporation, calculated by Penman formulation, and observed evaporation is associated with the ratio between the difference of temperature of water and air and saturation deficit of air, with a determination coeficient R2 = 0,79.