Seismic reflection profiles from the Southern Nares Abyssal Plain and the Madeira Abyssal Plain show faultlike displacements of subbottom reflections in areas of thickest sediment accumulation. A remarkable aspect of these faults on the crests of basement highs is that their displacement is reverse rather than normal. We propose that these faults are primarily the result of dewatering processes and that the apparent reverse faults around basement highs reflect more extensive dewatering, hence greater compaction of the sediments overlying the basement high. Estimates of cumulative compaction with depth demonstrate that these abyssal plain sediments may have been reduced in thickness by as much as 120 m over the present 300 m. This could have been accompanied by an average rate of water explusion of 0.02 m3 m-2 yr-1. This evidence of instability of abyssal plain sediments has important implications in terms of evaluating the concept of using these sediments as a disposal medium for high-level radioactive waste.