New seawater density measurements were made as a function of temperature T =(273.15 to 363.15) K and salinity (5 to 70 g kg-1). The measurements (N=230) from T =273.15 to 313.15K and Practical Salinity (S) from 0 to 40 were found to be in good agreement (∂=0.0036 kgm-3) with the equation of state of seawater (Millero and Poisson, 1981) made on samples with a known chlorinity (Cl). These results indicate that the Practical Salinities (S) are in agreement to within ±0.003 kgm-3 with the values calculated from the Chlorinity, SCl=1.80655 Cl. The measurements from 298.15 to 363.15 were used to extend the equation of state to high temperatures and salinities. All the densities were made relative to pure water (ρ- ρ0 where ρ0 is the density for pure water) were fitted to equations of the form (ρ - ρ0)/(kgm-3) = ASA + BSA1.5 + CSA2 where A, B, and C are functions of temperature and SA (g kg -1) is the absolute salinity, SA=(35.16504/35) S g kg -1. The fitted results from SA=0 to 50 g kg-1 and T =273.15 to 313.15K (N=242) gave standard errors of 0.0037 kgm -3. The fitted results from 298.15 to 363.15K (N=280) gave standard errors of 0.0063 kgm-3 and all the results (N=522) from 273.15 to 363.15K gave standard errors of 0.0063 kgm-3. The earlier density measurements (Millero et al., 1976b; Poisson et al.,1980) used to determine the equation of state of seawater (Millero and Poisson, 1981) were combined to derive equations that are valid from 273.15 to 313.15K and 273.15 to 363.15 K. The standard errors of these fits are respectively, 0.0038 kgm-3 (N=713) and 0.0063 kgm-3 (N=962). These new measurements expand the equation of state of seawater to a wider range of temperature (273.15 to 363.15)K and absolute salinity (0 to 70 kgm-3).
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