Apparent molar volumes V-Phi ,V-S were determined for sodium octyl, decyl, and dodecyl sulfates in water at 2 and 19 MPa from 25 to 130 degreesC. The shapes of vs the surfactant concentration curves depend on the surfactant alkyl chain, temperature and pressure. The standard partial molar volumes were calculated from data in the premicellar region whereas the partial molar volumes of the surfactant in the micellar phase were obtained from data in the postmicellar region. The partial molar expansibility and compressibility were evaluated from the dependence of the partial molar volume on temperature and pressure, respectively. Attention was focused to the expansibility and its pressure coefficient since studying the pressure effect on the expansibility is equivalent to studying the temperature effect on the compressibility. The hydrophilic and the hydrophobic (methylene group) contributions to the expansibility were evaluated. The comparison between the present and the alkyltrimethyl ammonium bromides data evidenced that, contrarily to the expectation, the pressure effect on the expansibility (or temperature effect on compressibility) is the same for the two polar heads in the micelles and independent of the nature solvent (micelles or water) for -SO4-Na. The pressure effect on the methylene group expansibility does not depend on the polar head in the micelles whereas it does in water. At a given temperature and pressure, the volume of micellization DeltaV(m) was calculated by assuming the pseudo-phase transition model. DeltaV(m) decreases with temperature according to the negative expansibility of micellization. The temperature at which DeltaV(m) assumes a null value depends on pressure and on the nature of the surfactant. In particular, at a given pressure, the inversion of the DeltaV(m) sign occurs at lower temperature the longer the alkyl chain is. Moreover, for each surfactant, DeltaV(m) shows a sign inversion at lower temperature by increasing pressure.