The speed of sound in standard seawater (diluted with pure water and evaporated) have been measured relative to pure water with a Nusonics single‐transducer sound velocimeter as a function of salinity (5–40°/00), temperature 0°–40°C, and applied pressure (0–1000 bars). The effect of pressure on the relative speeds of sound, (UP−UPH2O) ‐UO−UOH2O), have been fitted to an equation of the form (with a standard deviation of 0.19 msec−1) (UP−UPH2O) ‐ (UO−UOH2O) =AS(°/oo)+BS(°/oo)3/2+CS(°/oo)2, whereUandUH20are the speeds of sound in seawater and pure water, respectively; superscriptsPandOare used to denote applied pressurePandO(1 atm);A,B, andCare temperature‐ and pressure‐dependent parameters;S(o/oo) is the salinity in parts per thousand. This equation has been combined with the refitted high‐pressure pure‐water sound‐speed equation of Wilson [Naval Ordnance Lab. Rep.(1959)], Chen and Millero [J. Acoust. Soc. Am. 60, 1270–1273 (1976)], and the 1‐atm seawater sound‐speed data of Millero and Kubinski [J. Acoust. Soc. Am. 57, 312–319 (1975)] to calculate the speeds of sound for seawater at various salinities, temperatures, and pressures. Our results agree with the work of Wilson on the average to 0.36 msec−1over the range of 5 to 40o/oo salinity, 0° to 30°C, and 0 to 1000 bars. Over the oceanic range our results agree on the average with the work of Wilson to 0.3 msec−1(maximum deviation 0.6 msec−1), and with the work of Del Grosso to 0.5 msec−1(maximum deviation 0.9 msec−1). The better agreement of our results with those of Wilson may be fortuitous since our measurements were made relative to his pure‐water data.