Extensive sampling and logging of several holes on the downflexed northern margin of the Moresby rift basin allowed the processes of sediment compaction and diagenesis to be studied. One of the puzzling observations made during Leg 180 is the occurrence of zones of high porosity that deviate from the classical exponential decrease with depth. These zones of high porosity are of special interest since they are potentially affected by overpressure (Shipboard Scientific Party, 1999). By comparing simulated porosity changes with measured porosity data, Stover et al. (in press) argue that poroelastic deformation is likely to be the dominant mechanism for compaction, whereas viscoelastic compaction may significantly contribute in areas of high porosities. At Site 1109, the analytical solutions developed by Stover et al. allow one to predict overpressures of the order of 1MPa only in the high-porosity zones, a result confirmed by Kemerer and Screaton (this volume) at Site 1108. Therefore, significant overpressures do not seem—from these theoretical results—to occur. In addition, lithology appears to exert a strong control on permeability, since the reported value of 10-16 m2 in a sand layer at Site 1108 (Kemerer and Screaton, this volume) is ~20 times larger than the value in silty claystones (Bolton et al., 2000). Kemerer and Screaton suggest that lateral fluid migration in such sandy layers, whose occurrence is common, may be an efficient way to lower pressures within the basin.