Abstract Mass transport complexes (MTCs) within the Quaternary section of the ultra-deep water Nile Fan, offshore Egypt, form a significant portion of the Quaternary sedimentary section. This indicates the importance of mass-failure processes in deep water fan progradation. Regional mapping within the western platform of the Nile Fan reveals MTCs generally comprise 30%, but locally up to 94% of the Quaternary sedimentary column. Interpretation of the Quaternary section (upper 1 km of sediment) of a recently acquired, large, 3D seismic survey on the Nile Fan reveals the presence of five large mass transport complexes (MTCs) on the mid-slope of the western platform of the Nile Fan. These MTCs are on average 150 ms thick, but can obtain thicknesses of up to 357 ms. One of the MTCs is 175 km in length from the upper to the lower slope and comprises approximately 670 km3 of sediment. Introduction Slope failure deposits are common features of continental margins around the world1. Despite the fact that they are considered destructive sedimentary processes, their relevance to margin progradation is becoming increasingly recognized. Margin progradation is perhaps best studied in areas where, it is accelerated in high sedimentation rate environments, such as the deep water fan systems. The Nile Fan is the one of the largest deep water fans in the world. In ultra-deep water, the Quaternary section is in excess of 1 km thick. It is the objective of this study to investigate the architecture of the Quaternary section of the deep water Nile fan, and to understand the role of mass transport processes in the construction and progradation of the fan system. Slope failure is generally recognized by identifying escarpments, unconformities, and sedimentary deposits with certain characteristics suggesting mass transport (e.g., hummocky surfaces and incoherent internal reflections). Without referring to a specific physical process or depositional style, these deposits are referred to as mass transport complexes (MTCs). Large mass transport complexes are considered to be those that are generally greater that 2500 km2 in area and up to several hundreds of metres thick. The deep water continental slope environment has been studied for some time, but it is only recently that the oil and gas industry has become interested in these areas for their enormous hydrocarbon potential. This interest, combined with seismic imaging improvements and widespread availability of 3D seismic data, has resulted in large 3D seismic surveys of continental slope margins worldwide. From an industry perspective, research conducted using these datasets, has greatly improved understanding of turbidite channel and levee systems. Other important elements of deep water depositional system, such as the role and significance of MTCs, have been overlooked. A large 3D seismic data set has been acquired over the Nile Fan (Figure 1) and will provide the foundation for this investigation.