Evaporation rates were determined for seven brines whose average specific gravities varied from 1.207 to 1.333. Evaporation of the brines ranged from 70% to 9.5%, respectively, of the freshwater evaporation rate. The field data agree exceptionally well with differential vapor pressures over Great Salt Lake brine, measured in the laboratory by Dickson et al. [1965]. Water occasionally condenses on the heavier brines because of an inverted vapor pressure gradient.