The high pressure specific volumes of seawater (relative to pure water and 1 atm) have been measured from 0 to 40°C, 0 to 1000 bars and 5 to 40 ‰ salinity with a high pressure magnetic float densimeter (Millero, Knox and Emmet, Journal of Solution Chemistry, 1, 173-186, 1972). The results of the measurements have been fitted to a secant bulk modulus (K) equation of state K = V0P/(V0 - VP) = K0 + AP + BP2, where V0 and VP are the measured specific volumes of seawater at applied pressure zero and P, respectively, K0 = 1/βo, the reciprocal of the isothermal compressibility at atmospheric pressure, A and B are all salinity- and temperature-dependent parameters. The specific volumes have been fitted to this equation with a standard deviation of 7 ppm (on the measurement residuals) over the entire salinity, temperature and pressure range. The fitted relative specific volumes (VP - V0) are in excellent agreement (within ±5 ppm) with the sound-derived data of Wang and Millero (Journal of Geophysical Research, 78, 7122-7128, 1973) over the oceanographic range of salinity, temperature and pressure. The derived P-V-T properties have been compared with the experimental work of Ekman (Publications de circonstance. Conseil permanent international pour l'exploration de la mer, 43, 1-47, 1908); Wilson and Bradley (Deep-Sea Research, 15, 355-363, 1968); Bradshaw and Schleicher (Deep-Sea Research, 17, 691-706, 1970; personal communication 1974); Duedall and Paulowich (Review of Scientific Instruments, 44, 120-127, 1973); Emmet and Millero (Journal of Geophysical Research, 79, 3463-3472, 1974) and the sound-derived data of Wang and Millero (1973); Fine, Wang and Millero (Journal of Marine Research, 32, 433-456, 1974).
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