The goal of this project was to update pan evaporation coefficient (KP) values for the seven University of Puerto Rico Experimental Substations, based on updated pan evaporation data and the Penman-Monteith reference evapotranspiration. As a part of the study, historical pan evaporation data were evaluated from seven experimental substations. Significant decreasing pan evaporation was observed at Lajas and Río Piedras. Significant increasing pan evaporation was observed at Gurabo and Adjuntas, and no significant trends were observed at Fortuna, Isabela or Corozal. A significant difference was found to exist between the mean Kp values calculated with pan evaporation data from 1960 to 1980 and those with data from 1981 to 2000.