The concession of Petroleum Development Oman (PDO) is covered with some 30,000 square kilometres of 3-D seismic data, consisting of some 90 individual surveys, acquired and processed since 1984. With the 3-D coverage rapidly growing, more and more continuous coverage over large parts of the PDO concession is established. Traditionally surveys were processed on a survey-by-survey basis, incorporating some data from neighbouring surveys whenever possible. This approach resulted in a patchwork of often overlapping stand-alone 3-D projects, all with different datums, amplitude normalisations and processing histories. PDO strongly believes in the value of large integrated interpretation projects and the information that can be gained by using them. In order to achieve this the 3-D MegaProject was conducted during part of 1996 and 1997. As part of the 3-D MegaProject all 3-D seismic surveys acquired to date by PDO have been harmonised and merged. The concession area has been split up into four separate 3-D MegaGrids according to the dominant acquisition direction. Within each MegaGrid a consistent in-line and crossline numbering is used. The data are stored in cubes of 10 by 10 kilometres, referred to as MegaCells, which serve as the 3-D seismic data library. In the future, processing and merging of newly-acquired seismic data will follow the same procedures according to the common framework of MegaCells.