"Hourly class-A pan evaporation was measured for two oil shale process waters and compared to a fresh water control at a Laramie, Wyoming research site. The two oil shale process waters were shown to evaporate 9.9 and 18.3 percent slower than fresh water. An hourly evaporation equation was developed based on four meteorological parameters. The hourly model was found to compare favorably with measured pan evaporation. A rule of thumb equation was developed to predict evaporation of low quality waters based on pan water temperatures."