Pressure-volume-temperature (PVT) measurements were performed on alpha,omega-bis[(4,4’-cyanobiphenylyl)oxy]alkane (CBA-n) dimer liquid crystals having -O(CH2)(n)O- flexible spacers (n = 9, 10) between the 4,4’-cyanobiphenylyl ends. Both samples exhibit crystalline <----> nematic (CN) and nematic <----> isotropic (NI) transitions. The contribution in entropy Delta S-v caused by the volume change has been estimated by using the standard thermodynamic relation Delta S-v = -(alpha/beta)Delta V-tr, where Delta V-tr, represents the transition volume, alpha the thermal expansion coefficient, and beta the isothermal compressibility. The transition entropy (Delta S-tr)(v) at constant volume was elucidated by subtracting Delta S-v from the entropy change (Delta S-tr)(p) observed under constant pressure. By using the (Delta S-ni)(p) values derived from the Clapeyron equation, the constant-volume entropies (Delta S-ni)(v) at the NI transition were found to be 7.9 and 13.3 J mol(-1) K-1, respectively, for CBA-9 and -10. The values of(Delta S-cn)(v) for the CN transition were estimated on the basis of DSC data : 53.9 (CBA-9) and 62.4 J mol(-1) K-1 (CBA-10). For both transitions, the correction for the volume change was found to be significant, ranging from 40 to 60% of the total transition entropy observed under constant pressure. Nevertheless, the odd-even character of the NI transition remains unaltered. As shown by comparison of (Delta S-en)(v) and (Delta S-ni)(v), the major change (85%) takes place at the CN transition, the liberation of entropy at the NI interphase being much smaller (15%).