An extensive set of measurements made along a transect of the Atlantic Ocean covering a latitude range of between 52 ¿N and 20 ¿S have been used to investigate the characteristics of the bulk (BSST) minus skin (SSST) sea surface temperature difference (ΔT). ΔT is highly variable and has an overall mean value of 0.35 K¿0.35 K, a daytime mean value of 0.49 K¿0.39 K and a nighttime mean value of 0.27 K¿0.28 K. ΔT in all cases has no dependence on the amount of cloud cover. At low wind speeds, ΔT increases as the wind speed increases. At a wind speed >10 m s-1, wind induced turbulence reduces ΔT to a mean value of zero, and there is no evidence of any further wind speed dependency. The fact that a negligible ΔT exists in high wind speed conditions suggests that it can be appropriate to use BSST observations to validate satellite SSST measurements and that these are the preferred conditions in which to merge satellite-derived SSST and pseudo-BSST data. The variability of ΔT found in the data indicate that it is unwise to assume a mean global ΔT of 0.3 K. A comparison between several parameterizations of ΔT shows that such parameterizations are unable to describe the ΔT values found in this data set.¿ 1997 American Geophysical Union