Recently a new international standard for the thermodynamic properties of seawater, the Thermodynamical Equation of Seawater-2010 (TEOS-10), has been developed. For some properties it is valid at the high temperatures and salinities that may be found in industrial and desalination processes. However, precise in situ estimates of mass fraction salinities, derived from measurements of electrical conductivity in TEOS-10 using a modification of the Practical Salinity Scale 1978 (PSS-78), have been validated only when temperatures are less than 35 degrees C and salinities are less than 42 g/kg. The algorithm has not been validated at higher temperatures and salinities. Here a combination of numerical modeling and measurements is used to determine the electrical conductivity of high salinity and high temperature seawater. It is found that the TEOS-10 salinity algorithm can be used without other corrections to estimate seawater salinities from electrical conductivity for all temperatures between freezing and boiling and all salinities up to the point of calcite precipitation with an accuracy of 1% to 2% or better. (c) 2012 Elsevier By. All rights reserved.