The propagation of Rayleigh waves along 44 direct paths across the Pacific Ocean is studied and a regionalization of the dispersion according to the age of the sea floor is performed. The group velocity dispersion curves characteristic of each one of four age regions considered are obtained for periods up to 300 s. These curves show an increase of group velocities with age over the whole period range considered. The shear wave velocity models inferred yield a lithosphere thickening with age and show the presence below the lithosphere of two zones where negative velocity anomalies decrease with increasing age: the low velocity zone and a zone at a depth of 350 km.