A summary is presented of the available physical property data on 94 molten fluoride salt mixtures which have been evaluated for utilization as high temperature fluid fuels and reactor coolants. The specific physical properties which were either measured or calculated include density, heat capacity, heat of fusion, enthalpy, viscosity, thermal conductivity, and electrical conductivity. The experimental techniques and apparatus used in making the measurements are described, and the probable experimental errors are given. Some of the problems and potentialities of reactor systems using molten salt fuels and coolants are also briefly discussed.