Sediment deformation, changes in physical properties, and fluid migration can be studied under well-defined conditions in accretionary prisms. Our investigations focused on the accretionary prisms of Barbados (Caribbean) and Nankai (Japan) to interpret the effects of compaction on different lithologies during accretion. The interpretation is based on very good quality logging-while-drilling data. Statistical data analysis is used to determine sediment composition and its specific physical properties. Finally, the sediments are decompacted to determine the initial compaction before accretion and thus to quantify both the lateral and the vertical compaction components. This investigation shows that different lithologies undergo similar compaction and porosity reduction. The porosity differences of selected sediment layers between adjacent sites are significantly lower in Nankai than in Barbados, which implies higher fluid expulsion in Nankai. Decompaction of these sediment layers proves that the lateral compaction component is higher than the vertical compaction component.