Fluid inclusions from marine halities have long been studied to determine the chemical composition of ancient seawater. Chemical analysis of the major ions in fluid inclusions in halites from the solar saltwork of Great Inagua Island. Bahamas, and from the supratidal sabkha, Baja California. Mexico, show that modern marine halites faithfully record the chemical signature of water signature of water. The major ions in Great Inagua and Baha California fluid inclusions display distinctive linear trends when plotted againts one another (ie., Na+,K+, and SO2-4 -vs. Mg2+ and CI-), which track the evaporation path of seawater as it evolved during the crystallization of halite. These evaporation paths defined for the major ions by fluid inclusions in halite overlap findings of computer simulations of the evaporation of modern seawater by the Harvie, Melter, and Weare (HMW) computer program. The close match between the HMV seawater evaporation paths and the Great Inagua fluid inclusion data is not suprising considering the carefully controlled inflow, evaporation, and discharge of seawater at the Great Inagua saltwork. The major ion major chemistry of fluid inclusions from the Baja California halites matches the HMW seawater evaporation paths in most respects, but one Baja fluid inclusion has lower concentrations of Mg2+ Than evaporated seawater. Nonmarine inflows and syndepositional recycling of preexisting salts in the Baja California supratidal setting were not large enough to override the chemical signature of evaporating seawater as the primary control on the Baja Fluid inclusion compositions Fluids inclusions in halities from the nonmarine Qaighai Province, western china, have a distincly different major ion chemical signature than does "global" seawater. The fluid inclusions chemistries from the Qaidam Basin halites do not lie on the evaporation pathways defined by modern seawater and can clearly be differentiated from fluid inclusions containing evaporated seawater. If fluid inclusions in halites from modern natural settings contain unmistakable samples of evaporated seawater, then evaluation of the chemistry of ancient seawater by chemical analysis of fluid inclusions in ancient marine halites by means of the same approach should be valid.